升级Xode导致CocoaPods不可用，升级CocoaPods解决
由于升级了Xcode9，导致CocoaPods安装第三方库的时候报错，RuntimeError - [Xcodeproj] Unknown object version.
提示内容：
Search for existing GitHub issues similar to yours:
https://github.com/CocoaPods/CocoaPods/search?q=%5BXcodeproj%5D+Unknown+object+version.&type=Issues
https://github.com/CocoaPods/CocoaPods/search?q=%5BXcodeproj%5D+Unknown+object+version.&type=Issues
If none exists, create a ticket, with the template displayed above, on:
https://github.com/CocoaPods/CocoaPods/issues/new
https://github.com/CocoaPods/CocoaPods/issues/new
Be sure to first read the contributing guide for details on how to properly submit a ticket:
https://github.com/CocoaPods/CocoaPods/blob/master/CONTRIBUTING.md
https://github.com/CocoaPods/CocoaPods/blob/master/CONTRIBUTING.md
查看一下当前pod版本为1.0.1
升级版本:sudo gem install cocoapods并输入密码
升级成功之后，再次使用pod install导入第三方库，完成。