pod install 报错 RuntimeError - [Xcodeproj] Unknown object version

### Error

```
RuntimeError - [Xcodeproj] Unknown object version.
/Users/zhanglinfeng/.rvm/gems/ruby-2.4.0@global/gems/xcodeproj-1.19.0/lib/xcodeproj/project.rb:227:in `initialize_from_file'
/Users/zhanglinfeng/.rvm/gems/ruby-2.4.0@global/gems/xcodeproj-1.19.0/lib/xcodeproj/project.rb:112:in `open'
/Users/zhanglinfeng/.rvm/gems/ruby-2.4.0@global/gems/cocoapods-1.10.1/lib/cocoapods/installer/analyzer.rb:1186:in `block (2 levels) in inspect_targets_to_integrate'

这个错误大概是cocoapod和xcode的版本不对应，所以要对cocoapod进行升级。在终端执行下面的语句：

sudo gem install cocoapods --pre

 -----分割-----

后来又出事了，当初升级的ruby 2.7某天突然回到了2.4版本。又报上面那个错。这次只升级了ruby就正常了