Remove async from dev_dependencies.

pkgs/watcher/pubspec.yaml

diff --git a/pkgs/watcher/pubspec.yaml b/pkgs/watcher/pubspec.yaml
index ce64478..71a94df 100644
--- a/pkgs/watcher/pubspec.yaml
+++ b/pkgs/watcher/pubspec.yaml
@@ -8,11 +8,10 @@
 environment:
   sdk: '>=1.9.0 <2.0.0'
 dependencies:
-  async: '^1.2.0'
+  async: '^1.8.0'
   collection: '^1.0.0'
   path: '>=0.9.0 <2.0.0'
 dev_dependencies:
-  async: '^1.8.0'
   benchmark_harness: '^1.0.4'
   scheduled_test: '^0.12.0'
   test: '^0.12.0'