iOS CocoaPods 的安装流程

   //1.移除现有Ruby默认源
    gem sources --remove https://rubygems.org/
    //2.使用新的源
    gem sources -a https://ruby.taobao.org/
    //3.验证新源是否替换成功
    gem sources -l
    //4.安装CocoaPods
    (1)sudo gem install -n /usr/local/bin cocoapods
    (2)pod setup
    //5.更新gem
    sudo gem update --system