Prioritize index.css over the implicit App.css (facebook#2470)

packages/react-scripts/template/src/index.js

@@ -1,8 +1,8 @@
 import React from 'react';
 import ReactDOM from 'react-dom';
+import './index.css';
 import App from './App';
 import registerServiceWorker from './registerServiceWorker';
-import './index.css';
 
 ReactDOM.render(<App />, document.getElementById('root'));
 registerServiceWorker();