Laravel : Your requirements could not be resolved to an installable set of packages

I am trying to install Laravel in local system and i am getting error.

OS : ubuntu 12.04 LTS

Webserver : Nginx

PHP : PHP 5.3.10

step 1 :

$ git clone https://github.com/laravel/laravel.git my_project

step2 :

my_project$ composer install

I am getting following error.

Loading composer repositories with package information
Installing dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - laravel/framework v4.2.1 requires php >=5.4.0 -> no matching package found.
    - laravel/framework v4.2.0 requires php >=5.4.0 -> no matching package found.
    - Installation request for laravel/framework 4.2.* -> satisfiable by laravel/framework[v4.2.0, v4.2.1].

Potential causes:
 - A typo in the package name
 - The package is not available in a stable-enough version according to your minimum-stability setting
   see <https://groups.google.com/d/topic/composer-dev/_g3ASeIFlrc/discussion> for more details.

Read <http://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.