Roll mojo and sky pub versions to 0.0.4

TBR=hansmuller@chromium.org

Review URL: https://codereview.chromium.org/1074933003

packages/flutter/pubspec.yaml

@@ -2,6 +2,6 @@ name: sky
 author: Chromium Authors <sky-dev@googlegroups.com>
 description: Dart files to support executing inside Sky.
 homepage: https://github.com/domokit/mojo/tree/master/sky
-version: 0.0.3
+version: 0.0.4
 dependencies:
   mojo: '>=0.0.1 <1.0.0'