Add @override to starter template

packages/flutter_tools/templates/create/lib/main.dart.tmpl

diff --git a/packages/flutter_tools/templates/create/lib/main.dart.tmpl b/packages/flutter_tools/templates/create/lib/main.dart.tmpl
index 3acf224..618bc1f 100644
--- a/packages/flutter_tools/templates/create/lib/main.dart.tmpl
+++ b/packages/flutter_tools/templates/create/lib/main.dart.tmpl
@@ -20,6 +20,7 @@
 }
 
 class FlutterDemo extends StatefulWidget {
+  @override
   _FlutterDemoState createState() => new _FlutterDemoState();
 }
 
@@ -32,6 +33,7 @@
     });
   }
 
+  @override
   Widget build(BuildContext context) {
     return new Scaffold(
       appBar: new AppBar(