[Flutter]CocoaPods installed but not working の対処法

エラー内容

$ flutter doctor

以下のエラー

[!] Xcode - develop for iOS and macOS (Xcode 12.2)
    ✗ CocoaPods installed but not working.
        You appear to have CocoaPods installed but it is not working.
        This can happen if the version of Ruby that CocoaPods was installed with is different from the one
        being used to invoke it.
        This can usually be fixed by re-installing CocoaPods. For more info, see
        https://github.com/flutter/flutter/issues/14293.
      To re-install CocoaPods, run:
        sudo gem install cocoapods

解決方法

参考

$ sudo gem uninstall cocoapods //不必要?
$ sudo gem install -v1.8.4 cocoapods -n /usr/local/bin