cocoapods的安装

＊首先，执行以下命令删除原来的ruby源：
gem sources --remove https://rubygems.org/
执行命令后可在终端看见以下信息：
https://rubygems.org/ removed from sources
＊然后下一步添加你找到的可用的镜像源
gem sources -a https://gems.ruby-china.org/
＊验证新源是否替换成功
gem sources -l
终端输出:
*** CURRENT SOURCES ***
https://gems.ruby-china.org/
到此ruby 源替已经换成国内的源
sudo gem install -n /usr/local/bin cocoapods 安装