Fix build after hixie's rename

TBR=ianh@google.com

Review URL: https://codereview.chromium.org/1164073002

examples/fn2/container.dart

@@ -7,7 +7,7 @@ import 'package:sky/framework/fn2.dart';
 import 'package:sky/framework/rendering/box.dart';
 import '../lib/solid_color_box.dart';
 
-class Rectangle extends RenderNodeWrapper {
+class Rectangle extends RenderObjectWrapper {
   RenderSolidColorBox root;
   RenderSolidColorBox createNode() =>
       new RenderSolidColorBox(color, desiredSize: new sky.Size(40.0, 130.0));

examples/game/lib/sprite_box.dart

@@ -49,7 +49,7 @@ class SpriteBox extends RenderBox {
     }
   }
 
-  void paint(RenderNodeDisplayList canvas) {
+  void paint(RenderObjectDisplayList canvas) {
     // Move to correct coordinate space before drawing
     double scaleX = 1.0;
     double scaleY = 1.0;