Pin firebase_auth to specific google_sign_in version

Author: goderbauer

packages/firebase_auth/example/pubspec.yaml

@@ -6,9 +6,7 @@ dependencies:
     sdk: flutter
   firebase_auth:
     path: ../
-  # TODO(jackson): Point this at pub once a stable version is published
-  google_sign_in:
-    git: git://github.com/flutter/google_sign_in
+  google_sign_in: 0.0.1
 
 flutter:
   uses-material-design: true