更新：最近在更新Mac系统到macOS High Sierra后，pod install 出现下面提示：
-bash: /usr/local/bin/pod: /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby: bad interpreter: No such file or directory
之后经过查询得知，可以这样解决问题
sudo gem update --system sudo gem install -n /usr/local/bin cocoapods