react-native run-androidでエラー

こんなエラーが出る

Building and installing the app on the device (cd android && gradlew.bat installDebug)...
エラー: メイン・クラスorg.gradle.wrapper.GradleWrapperMainが見つからなかったかロードできませんでした
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

対策

cd android

gradle wrapper

cd ..

react-native run-android