feat: Add counter increment value to 4

lib/main.dart

@@ -64,7 +64,7 @@ class _MyHomePageState extends State<MyHomePage> {
       // so that the display can reflect the updated values. If we changed
       // _counter without calling setState(), then the build method would not be
       // called again, and so nothing would appear to happen.
-      _counter = _counter + 2;
+      _counter = _counter + 4;
     });
   }