XZ_iOS之更新cocoaPods出现错误ERROR: While executing gem ... (Gem::FilePermissionError)

拉取项目之后，使用 pod install 拉取第三方代码的时候出现下面错误

[!] The version of CocoaPods used to generate the lockfile (1.5.0) is higher than the version of the current executable (1.3.1). Incompatibility issues may arise.

更新cocoaPods，终端输入：sudo gem install cocoapods

之后，又出现了下面的错误：

ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /usr/bin directory.

终端输入：sudo gem install -n /usr/local/bin cocoapods

输入密码，执行结果如下图：

这次终于解决了，再次在终端输入pod install 时，出现了下图结果，说明cocoaPods可以正常使用了：