新建了一个项目，在项目里创建了Podfile文件，使用pdo install命令无法安装成功，报错信息如下：
[!] Oh no, an error occurred.
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Looking for related issues on cocoapods/cocoapods...
RuntimeError - [Xcodeproj] Unknown object version.
https://github.com/CocoaPods/CocoaPods/issues/7458 [closed] [17 comments]
4 weeks agoRuntimeError - [Xcodeproj] Unknown object version.
https://github.com/CocoaPods/CocoaPods/issues/6992 [closed] [15 comments]
6 weeks agoPod Update: RuntimeError - [Xcodeproj] Unknown object version. Xcode Beta 5
https://github.com/CocoaPods/CocoaPods/issues/8003 [closed] [18 comments]
29 Oct 2018
and 43 more at:
https://github.com/cocoapods/cocoapods/search?q=[Xcodeproj]%20Unknown%20object%20version.&type=Issues&utf8=✓
各种折腾，还删除了cocoapods，结果装不上了，后来才发现镜像源域名(https://gems.ruby-china.org/)换了,更改为了https://gems.ruby-china.com/
解决办法：
gem sources -l 查看当前是什么连接
gem sources --remove https://gems.ruby-china.org/ 然后移除旧源，改用新源
gem sources -a https://gems.ruby-china.com/
再重新安装cocoapods ： sudo gem install cocoapods
成功安装后查看版本 xcodeproj --version 显示为1.7.0
这时通过pod install命令即可成功安装
