moved cubes to rotating group to show the effect in the animation

examples/webgl_loader_imagebitmap.html

@@ -151,7 +151,7 @@
 				group.add( new THREE.GridHelper( 4, 12 ) );
 
 				cubes = new THREE.Group();
-				scene.add( cubes );
+				group.add( cubes );
 
 				addImageBitmap();
 				addImage();