安装 composer global require 报超时错误，大神帮看看。 [ 2.0 版本 ]

安装 composer global require "fxp/composer-asset-plugin:1.0.0"时报以下错误，找不出原因。

Changed current directory to /root/.composer
./composer.json has been updated
Loading composer repositories with package information
The "https://packagist.org/packages.json" file could not be downloaded: failed to open stream: Connection timed out
https://packagist.org could not be fully loaded, package information was loaded from the local cache and may be out of date
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - The requested package fxp/composer-asset-plugin could not be found in any version, there may be a typo in the package name.

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.

Installation failed, reverting ./composer.json to its original content.