Release 1.2.0.

Review URL: https://codereview.chromium.org//1212223002.
diff --git a/pubspec.yaml b/pubspec.yaml
index 102f2d4..1d8d181 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: async
-version: 1.2.0-dev
+version: 1.2.0
 author: Dart Team <misc@dartlang.org>
 description: Utility functions and classes related to the 'dart:async' library.
 homepage: https://www.github.com/dart-lang/async