想看个开源库，里面要求用cocoapods-keys，就照着上面的提示
sudo gem install cocoapods cocoapods-keys
但报错，提示权限不足。。。
Permission denied
或者一堆其它的。
Your Podfile requires that the plugin \cocoapods-keys` `
google了10多分钟之后，综合了一下答案如下：
chown -R $(whoami) ~/.gem
gem install cocoapods-keys --user-install
这cocoapods-keys是什么东东？
A key value store for enviroment and application keys.
Its good security practice to keep production keys out of developer hands. CocoaPods-keys makes it easy to have per-user config settings stored securely in the developer's keychain, and not in the application source. It is a plugin that once installed will run on every pod install or pod update
