运行react-native run-android 报错：
Building and installing the app on the device (cd android && ./gradlew installDebug...
Could not install the app on the device, read the error above for details.
Make sure you have an Android emulator running or a device connected and have
set up your Android development environment:
https://facebook.github.io/react-native/docs/android-setup.html
错误原因：
android/gradlew 没有执行权限
解决办法：
给gradlew 添加可执行权限
chmod +x android/gradlew
再次运行react-native run-android 可以正常安装程序
