使用composer遇到“Your requirements could not be”错误的解决办法：
Your requirements could not be resolved to an installable set of packages.
如果出现下面这种情况：
Loading composer repositories with package information Updating dependencies (including require-dev) Your requirements could not be resolved to an installable set of packages.
需要安装一个composer资源插件，运行命令安装即可：
composer global require "fxp/composer-asset-plugin:^1.4.1"
