Support plugins that conform to ES6 modules
Support plugins that conform to ES6 modules

Summary:
ES6 modules export an object with a property called `default`. See Babel itself for how this is handled: https://github.com/babel/babel/commit/b5b7e346a04c99da8793e2c65cc3b3c7c720253d
Closes https://github.com/facebook/react-native/pull/4513

Reviewed By: svcscm

Differential Revision: D2715512

Pulled By: mkonicek

fb-gh-sync-id: 40e5ea35adcdb66806a4895578d637cd72538619

almost/react-native,almost/react-native,almost/react-native,almost/react-native,almost/react-native,almost/react-native,almost/react-native,almost/react-native