Fix lints (#9307)

examples/flutter_gallery/lib/demo/material/full_screen_dialog_demo.dart

@@ -203,7 +203,7 @@ class FullScreenDialogDemoState extends State<FullScreenDialogDemo> {
                     });
                   }
                 ),
-                const Text('All-day')
+                const Text('All-day'),
               ]
             ),
             new Container(
@@ -221,7 +221,7 @@ class FullScreenDialogDemoState extends State<FullScreenDialogDemo> {
                       });
                     }
                   ),
-                  new Text('All-day')
+                  const Text('All-day'),
                 ]
               )
             )

packages/flutter/test/material/scaffold_test.dart

@@ -334,13 +334,13 @@ void main() {
       await tester.pumpWidget(
         new MaterialApp(
           theme: new ThemeData(platform: platform),
-          home: new Scaffold(appBar: new AppBar(), body: new Text('Page 1')),
+          home: new Scaffold(appBar: new AppBar(), body: const Text('Page 1')),
         )
       );
 
       tester.state<NavigatorState>(find.byType(Navigator)).push(new MaterialPageRoute<Null>(
         builder: (BuildContext context) {
-          return new Scaffold(appBar: new AppBar(), body: new Text('Page 2'));
+          return new Scaffold(appBar: new AppBar(), body: const Text('Page 2'));
         },
         fullscreenDialog: true,
       ));