淘宝镜像一直安装不成功（http还是https都一样）
坑1：gem sources --add https://ruby.taobao.org/ --remove https://rubygems.org/
坑2: gem sources --add https://gems.ruby-china.org/ --remove https://rubygems.org/
镜像：gem sources --add https://gems.ruby-china.com/ --remove https://rubygems.org/
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