Remove keys from the examples.

sky/examples/widgets/navigation.dart

Index: sky/examples/widgets/navigation.dart
diff --git a/sky/examples/widgets/navigation.dart b/sky/examples/widgets/navigation.dart
index a5e32000278a3ffe6ec86481fd80ab5b54f67a25..6f1d3d99bdf11d0ce5ffdb45a0784881ed7b8aaf 100644
--- a/sky/examples/widgets/navigation.dart
+++ b/sky/examples/widgets/navigation.dart
@@ -16,12 +16,10 @@ List<Route> routes = [
       child: new Block([
         new Text("You are at home"),
         new RaisedButton(
-          key: 'b',
           child: new Text('GO SHOPPING'),
           onPressed: () => navigator.pushNamed('shopping')
         ),
         new RaisedButton(
-          key: 'a',
           child: new Text('START ADVENTURE'),
           onPressed: () => navigator.pushNamed('adventure')
         )
@@ -36,12 +34,10 @@ List<Route> routes = [
       child: new Block([
         new Text("Village Shop"),
         new RaisedButton(
-          key: 'a',
           child: new Text('RETURN HOME'),
           onPressed: () => navigator.back()
         ),
         new RaisedButton(
-          key: 'b',
           child: new Text('GO TO DUNGEON'),
           onPressed: () => navigator.push(routes[2])
         )