在Digital Ocean上更新Composer时出现连接超时错误

我可以掉进小滴中。也能够进行更新和升级。

当我尝试运行sudo composer自我更新或composer更新时，出现连接超时错误。

The "https://getcomposer.org/versions" file could not be downloaded: failed to open stream: Connection timed out  

输出 ufw status

To      Action    From
22      ALLOW     Anywhere
80      ALLOW     Anywhere
443     ALLOW     Anywhere
25      ALLOW     Anywhere
10000   ALLOW     Anywhere     

输出 composer diagnose

Checking platform settings: OK
Checking git settings: OK
Checking http connectivity to packagist: FAIL
[Composer\Downloader\TransportException] The "http://packagist.org/packages.json" file    could not be downloaded: failed to open stream: Connection timed out
Checking https connectivity to packagist: FAIL
[Composer\Downloader\TransportException] The "https://packagist.org/packages.json" file    could not be downloaded: failed to open stream: Connection timed out
Checking github.com rate limit: OK
Checking disk free space: OK
Checking composer version: 

[Composer\Downloader\TransportException]                                     
The "https://getcomposer.org/version" file could not be downloaded: failed   
to open stream: Connection timed out

输出 composer --version

Composer version 1.0-dev (9e9c1917e1ed9f3f78b195a785aee3c6dc3cb883) 2015-11-23 10:31:23  

输出 curl IL http://packagist.org/packages.json

HTTP/1.1 200 OK
Server: nginx
Date: Sun, 10 Dec 2017 08:40:20 GMT
Content-Type: application/json
Content-Length: 1302
Last-Modified: Sun, 10 Dec 2017 08:38:28 GMT
Connection: keep-alive
ETag: "5a2cf284-516"
Cache-Control: private, max-age=0, no-cache
Accept-Ranges: bytes  

我尝试手动获取最新作曲家的副本，但它也无法正常工作

输出 php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"

PHP Warning:  copy(https://getcomposer.org/installer): failed to open stream: Connection timed out in Command line code on line 1  

可能是什么原因？大约一个星期前，我一直在工作。我可以访问（浏览）Droplet上托管的网页。也能够进行更新和升级。