x-code9 cocoapods 错误 RuntimeErro

升级 cocoapods 1.5.2

终端输入
sudo gem update –system
显示如下错误
ERROR: While executing gem … (Gem::FilePermissionError)
You don’t have write permissions for the /usr/bin directory.

网上看到解决方法：

重新输入下面
sudo gem install -n /usr/local/bin sass
sudo gem install -n /usr/local/bin cocoapods