部署失败，并显示以下错误：＃<NoMethodError：main：Object>的未定义方法“ on”

我打算将Rails应用程序部署到数字海洋。
我按照此https://gorails.com/deploy/ubuntu/14.04的教程进行操作
，然后在本地命令提示符下运行该命令以进行部署。

# cap production deploy

运行命令后，出现以下错误。

 /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/i18n.rb:4: warning: duplicated key at line 6 ignored: :starting
    ** Invoke production (first_time)
    ** Execute production
    ** Invoke load:defaults (first_time)
    ** Execute load:defaults
    ** Invoke bundler:map_bins (first_time)
    ** Execute bundler:map_bins
    ** Invoke deploy:set_rails_env (first_time)
    ** Execute deploy:set_rails_env
    ** Invoke deploy:set_linked_dirs (first_time)
    ** Execute deploy:set_linked_dirs
    ** Invoke deploy:set_rails_env 
    ** Invoke deploy (first_time)
    ** Execute deploy
    ** Invoke deploy:starting (first_time)
    ** Execute deploy:starting
    ** Invoke deploy:check (first_time)
    ** Execute deploy:check
    ** Invoke git:check (first_time)
    ** Invoke git:wrapper (first_time)
    ** Execute git:wrapper
    cap aborted!
    NoMethodError: undefined method `on' for main:Object
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/tasks/git.rake:16:in `block (2 levels) in <top (required)>'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:248:in `call'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:248:in `block in execute'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:243:in `each'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:243:in `execute'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:187:in `block in invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:180:in `invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:209:in `block in invoke_prerequisites'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:207:in `each'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:207:in `invoke_prerequisites'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:186:in `block in invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:180:in `invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:173:in `invoke'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/dsl.rb:14:in `invoke'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/tasks/deploy.rake:34:in `block (2 levels) in <top (required)>'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:248:in `call'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:248:in `block in execute'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:243:in `each'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:243:in `execute'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:187:in `block in invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:180:in `invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:173:in `invoke'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/dsl.rb:14:in `invoke'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/tasks/deploy.rake:4:in `block (2 levels) in <top (required)>'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:248:in `call'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:248:in `block in execute'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:243:in `each'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:243:in `execute'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:187:in `block in invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:180:in `invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:173:in `invoke'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/dsl.rb:14:in `invoke'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/tasks/framework.rake:65:in `block (2 levels) in <top (required)>'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/tasks/framework.rake:64:in `each'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/tasks/framework.rake:64:in `block in <top (required)>'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:248:in `call'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:248:in `block in execute'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:243:in `each'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:243:in `execute'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:187:in `block in invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:180:in `invoke_with_call_chain'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/task.rb:173:in `invoke'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/application.rb:150:in `invoke_task'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/application.rb:106:in `block (2 levels) in top_level'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/application.rb:106:in `each'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/application.rb:106:in `block in top_level'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/application.rb:115:in `run_with_threads'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/application.rb:100:in `top_level'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/application.rb:78:in `block in run'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/application.rb:176:in `standard_exception_handling'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/rake-11.1.1/lib/rake/application.rb:75:in `run'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/lib/capistrano/application.rb:15:in `run'
    /Users/llvc/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/capistrano-3.1.0/bin/cap:3:in `<top (required)>'
    /Users/llvc/.rbenv/versions/2.2.3/bin/cap:23:in `load'
    /Users/llvc/.rbenv/versions/2.2.3/bin/cap:23:in `<main>'
    Tasks: TOP => git:check => git:wrapper
    The deploy has failed with an error: #<NoMethodError: undefined method `on' for main:Object>
    ** Invoke deploy:failed (first_time)
    ** Execute deploy:failed

我从stackoverflow中发现了类似的问题。NoMethodError：main：Object的未定义方法“ on”，
但是解决方案无法帮助我。我需要专家的额外帮助。谢谢。斤