一、查看是否有已安装的镜像源
命令：gem sources -l
输出：
*** CURRENT SOURCES ***
https://gems.ruby-china.org/
二、将不可用的源 https://gems.ruby-china.org/ 换成 https://gems.ruby-china.com/
1)移除 https://gems.ruby-china.org/
命令：gem sources --remove https://gems.ruby-china.org/
2)换成 https://gems.ruby-china.com/
命令：gem sources -a https://gems.ruby-china.com/
输出：https://gems.ruby-china.com/ added to sources
三、安装cocoapods
安装之前先更新一下：
命令：sudo gem update--system
命令：sudo gem install -n /usr/local/bin cocoapods
以上已完成安装。
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若要修改源提速(以清华的镜像为例)：
cd ~/.cocoapods/repos
pod repo remove master
git clone https://mirrors.tuna.tsinghua.edu.cn/git/CocoaPods/Specs.git master
最后在podfile文件第一行添加：
source ‘https://mirrors.tuna.tsinghua.edu.cn/git/CocoaPods/Specs.git’
