Widen config search paths to include metro.config.cjs (facebook#1027)

Summary:
Pull Request resolved: facebook#1027

Resolves facebook#1026.

Changelog: **[Feature]** Widen config search paths to include `metro.config.cjs`

Reviewed By: robhogan

Differential Revision: D47290079

fbshipit-source-id: 3e46c954a1e1451558b14ed4558fede5f00200dd

packages/metro-config/src/loadConfig.js

@@ -46,13 +46,18 @@ function overrideArgument<T>(arg: Array<T> | T): T {
 }
 
 const explorer = cosmiconfig('metro', {
-  searchPlaces: ['metro.config.js', 'metro.config.json', 'package.json'],
-
+  searchPlaces: [
+    'metro.config.js',
+    'metro.config.cjs',
+    'metro.config.json',
+    'package.json',
+  ],
   loaders: {
     '.json': cosmiconfig.loadJson,
     '.yaml': cosmiconfig.loadYaml,
     '.yml': cosmiconfig.loadYaml,
     '.js': cosmiconfig.loadJs,
+    '.cjs': cosmiconfig.loadJs,
     '.es6': cosmiconfig.loadJs,
     noExt: cosmiconfig.loadYaml,
   },