解决 安装cocoapods失败，提示 requires Ruby version >=2.2.2

步骤如下：

rvm install ruby-2.2

但是，但是竟然报错了，具体我忘记额，但是是权限和brew的问题，那么我又转向修复brew：

// 清理原来brew
rm -rf /usr/local/Cellar /usr/local/.git && brew cleanup 

// 安装
ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

// 检查有无问题
brew doctor

brew解决后，我赶紧去试试rvm install ruby-2.2,但是提示：

Already installed ruby-2.2.4.
To reinstall use:

    rvm reinstall ruby-2.2.4

OK，换成rvm reinstall ruby-2.2.4，成功,再去试试安装cocoapods

sudo gem install -n /usr/local/bin cocoapods --pre

关键命令: 

$ rvm autolibs read-only # read more here: https://rvm.io/rvm/autolibs
$ rvm install ruby  # or any version you want