fix css path

Author: nicolasgarnier

example/src/App.jsx

@@ -19,7 +19,7 @@ import firebase from 'firebase/app';
 import 'firebase/auth';
 import { FirebaseAuth } from 'react-firebaseui';
 import styles from './app.css'; // This uses CSS modules.
-import './firebaseui-styling.global.css'; // Import globally.
+import './firebaseui-overrides.global.css'; // Import globally.
 
 // Get the Firebase config from the auto generated file.
 const firebaseConfig = require('./firebase-config.json').result;