Get the async package from the hosted source.

pubspec.yaml

Index: pubspec.yaml
diff --git a/pubspec.yaml b/pubspec.yaml
index ca3f387a0fab5a205ede0864541e00b520175fc7..ff0053980abde13bec0de49a8b2b121de12c375f 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: test
-version: 0.12.7-dev
+version: 0.12.7
 author: Dart Team <misc@dartlang.org>
 description: A library for writing dart unit tests.
 homepage: https://github.com/dart-lang/test
@@ -34,6 +34,3 @@ dependencies:
 dev_dependencies:
   fake_async: '^0.1.2'
   scheduled_test: '^0.12.2'
-
-dependency_overrides:
-  async: {git: git://github.com/dart-lang/async.git}