直接执行 sudo gem install cocoapods，会报错， ERROR: While executing gem ... (Errno::EPERM) Operation not permitted - /usr/bin/pod
替换成：sudo gem install -n /usr/local/bin cocoapods
然后又报错
WARNING: Unable to pull data from 'ruby.taobao.org/': bad response Not Found 404 (ruby.taobao.org/specs.4.8.g…)
网上查才知道 taobao 镜像已经改成 https 的了。
所以解决方案如下：
1、替换为淘宝镜像，注意是 https
gem sources -a ruby.taobao.org/
2、执行以下命令
sudo gem install -n /usr/local/bin cocoapods
