swift-Xcode7.1新建playground报错Unab

用Xcode7.1新建playground界面直接报错

Unable to find execution service for selected run destination

• 解决方法
• 1.关闭Xcode
• 2.在终端执行两行代码

rm -rf ~/Library/Developer/CoreSimulator/Devices

killall -9 com.apple.CoreSimulator.CoreSimulatorService