Update default template from .css to .scss files

Author: kmturley

packages/react-scripts/template/src/App.css renamed to packages/react-scripts/template/src/App.scss

@@ -1,5 +1,5 @@
 import * as React from 'react';
-import './App.css';
+import './App.scss';
 
 import logo from './logo.svg';
 

packages/react-scripts/template/src/App.tsx

@@ -1,7 +1,7 @@
 import * as React from 'react';
 import * as ReactDOM from 'react-dom';
 import App from './App';
-import './index.css';
+import './index.scss';
 import registerServiceWorker from './registerServiceWorker';
 
 ReactDOM.render(