Fix game to depend on Sky

Also updated the version range on stocks2.

https://github.com/domokit/mojo/issues/262

R=ianh@google.com

Review URL: https://codereview.chromium.org/1195933004.

examples/game/pubspec.yaml

 name: game
 dependencies:
-  box2d: any
+  sky: '>=0.0.10 <1.0.0'

examples/stocks2/pubspec.yaml

@@ -4,4 +4,4 @@ description: A demo application using Sky that shows stock data
 homepage: https://github.com/domokit/sky_sdk/tree/master/examples/stocks
 version: 0.0.1
 dependencies:
-  sky: '>=0.0.1 <1.0.0'
+  sky: '>=0.0.10 <1.0.0'