Update Sky package version

We need to pull in an updated version of sky_tools to get a version that
doesn't try to gzip everything.

packages/flutter/pubspec.yaml

 name: sky
-version: 0.0.22
+version: 0.0.23
 author: Chromium Authors <sky-dev@googlegroups.com>
 description: A framework for writing Sky applications
 homepage: https://github.com/domokit/sky_engine/tree/master/sky/sdk
@@ -12,7 +12,7 @@ dependencies:
   newton: ^0.1.0
   sky_engine: ^0.0.1
   sky_services: ^0.0.1
-  sky_tools: ^0.0.3
+  sky_tools: ^0.0.4
   vector_math: ^1.4.3
 environment:
   sdk: '>=1.8.0 <2.0.0'