Xcode10 CocoaPods 私有库校验时报错

ERROR | [iOS] unknown: Encountered an unknown error  
(Could not find a `ios` simulator (valid values:  
com.apple.coresimulator.simruntime.ios-11-1,  
com.apple.coresimulator.simruntime.ios-12-2,  
com.apple.coresimulator.simruntime.tvos-12-2, 
com.apple.coresimulator.simruntime.watchos-5-2).
Ensure that Xcode -> Window -> Devices has at least one `ios` 
simulator listed or otherwise add one.) during validation.

切换到官方源https://rubygems.org/，然后更新CocoaPods到 1.6版本就好了