https://github.com/react-native-community/react-native-cli/blob/v2.0.0/packages/cli/src/commands/server/runServer.js#L48
https://github.com/react-native-community/react-native-cli/blob/v2.0.0/packages/cli/src/tools/loadMetroConfig.js#L95
https://github.com/facebook/metro/blob/v0.53.1/packages/metro-config/src/loadConfig.js#L239
https://github.com/facebook/metro/blob/v0.53.1/packages/metro-config/src/loadConfig.js#L62
默认配置文件名
[
'metro.config.js',
'metro.config.json',
'package.json',
'rn-cli.config.js',
]
默认 react-native config
https://github.com/react-native-community/react-native-cli/blob/v2.0.0/packages/cli/src/tools/loadMetroConfig.js#L34
默认 metro config
https://github.com/facebook/metro/blob/v0.53.1/packages/metro-config/src/defaults/index.js