Update version in pubspec.yaml

pubspec.yaml

@@ -1,6 +1,6 @@
 name: chewie
 description: A video player for Flutter with Cupertino and Material play controls
-version: 0.9.3
+version: 0.9.4
 homepage: https://github.com/brianegan/chewie
 authors:
   - Brian Egan <brian@brianegan.com>