是react native 最新版本問題，下面兩組命令，隨便選一組。

npm uninstall react-native
npm install --save [email protected]
npm install --save babel-core@latest babel-loader@latest
npm uninstall --save babel-preset-react-native
npm install --save [email protected]
react-native run-android

==========或者======
//卸載最新版本

npm uninstall react-native
npm uninstall -g react-native-cli
//安裝
npm install [email protected]
npm install -g [email protected]
react-native run-android