iOS-ERROR | [iOS] unknown: Encou

执行 pod lib lint 时，报错：

ERROR | [iOS] unknown: Encountered an unknown error (Could not find a ios simulator (valid values: com.apple.coresimulator.simruntime.ios-10-3, com.apple.coresimulator.simruntime.ios-12-1, com.apple.coresimulator.simruntime.ios-8-1, com.apple.coresimulator.simruntime.tvos-12-1, com.apple.coresimulator.simruntime.watchos-5-1). Ensure that Xcode -> Window -> Devices has at least one ios simulator listed or otherwise add one.

解决方法：
升级CocoaPods（使用的gem 源： https://gems.ruby-china.com/）

sudo gem install cocoapods

再次执行 pod lib lint， 验证上面的错误通过