ERROR: While executing gem ... (Gem::FilePermissionError)
You don‘t have write permissions for the /Library/Ruby/Gems/2.0.0 directory.
系权限问题，命令行输入：
sudo gem install cocoapods，即可安装
cocoapods安装失败
原文：http://www.cnblogs.com/Rinpe/p/4922596.html
