Migrate RaisedButton -> ElevatedButton (#654)

* Migrate RaisedButton to ElevatedButton

* Add changelog entry

CHANGELOG.md

@@ -9,6 +9,7 @@
  - Enabling direct import of Sprite and SpriteAnimation
  - Renamed `Composition` to `ImageComposition` to prevent confusion with the composition component
  - Added `rotation` and `anchor` arguments to `ImageComposition.add`
+ - Change RaisedButton to ElevatedButton in timer example
 
 ## 1.0.0-rc6
  - Use `Offset` type directly in `JoystickAction.update` calculations

doc/examples/timer/lib/main.dart

@@ -12,12 +12,12 @@ class MyGameApp extends StatelessWidget {
   Widget build(BuildContext context) {
     return MaterialApp(routes: {
       '/': (BuildContext context) => Column(children: [
-            RaisedButton(
+            ElevatedButton(
                 child: const Text('Game'),
                 onPressed: () {
                   Navigator.of(context).pushNamed('/game');
                 }),
-            RaisedButton(
+            ElevatedButton(
                 child: const Text('BaseGame'),
                 onPressed: () {
                   Navigator.of(context).pushNamed('/base_game');