升级xcode10.3后打包问题。

SDK Version Issue. This app was built with the iOS 12.0 SDK. All iOS apps submitted to the App Store must be built with the iOS 11 SDK or later, included in Xcode 9 or later. Further, starting March 2019, all iOS apps submitted to the App Store must be built with the iOS 12.1 SDK or later, included in Xcode 10.1 or later.

解决办法：

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDK，删除iPhoneOS12.0.sdk