当前的Firebase 5.x至少需要CocoaPods版本1.4.0。如果您在升级CocoaPods之后仍然遇到问题，请将Podfile内容添加到问题中。

The current Firebase 5.x requires at least CocoaPods version 1.4.0. Add your Podfile contents to the question if you're still having problems after upgrading CocoaPods.