Xcode更新至10.3.1运行项目报错：
Failed to find or create execution context for description ' System content for IBCocoaTouchFramework-ElevenAndLater scaleFactor=2x'. These intermediate objects were non-nil:
尝试clean，强退Xcode重新运行，无效，网上搜索到解决方案：
sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService
在终端运行这一命令，重新run，搞定！感谢 xiaoshitou 提供的解决方案
