refactor(example): remove unnecessary cupertino import

Author: uxduck

push/example/lib/main.dart

@@ -1,5 +1,5 @@
 import 'package:flutter/material.dart' hide Notification;
-import 'package:flutter/cupertino.dart';
+import 'package:flutter/cupertino.dart' hide Notification;
 import 'package:flutter_hooks/flutter_hooks.dart';
 import 'package:flutter_local_notifications/flutter_local_notifications.dart';
 import 'package:push/push.dart';