small fix

lib/main.dart

@@ -70,12 +70,14 @@ class _MyHomePageState extends State<MyHomePage> {
     _grid = List.generate(widget.gridSize, (_) => List.generate(widget.gridSize, (_) => Random().nextInt(5)));
   }
 
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
         title: Text('Candy Crush'),
       ),
       body: Center(
+        child: Expanded(
           child: GridView.builder(
             shrinkWrap: true,
             gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
@@ -98,6 +100,7 @@ class _MyHomePageState extends State<MyHomePage> {
             },
           ),
         ),
+      ),
     );
   }