命令行更新(安装)步骤
$ sudo gem update --system // 先更新gem，国内需要切换源
$ gem sources --remove https://rubygems.org/
$ gem sources -a https://ruby.taobao.org/
$ gem sources -l
*** CURRENT SOURCES ***
http://ruby.taobao.org/
$ sudo gem install cocoapods // 安装cocoapods
$ pod setup
查看版本
$ pod --version