Declare support for async 2.0.0 (#92)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7101619..b26e554 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.15.2+12
+
+* Declare support for `async` 2.0.0.
+
 ## 0.15.2+11
 
 * Update `AssetNode.whenAvailable` to be a generic method to fix a new strong
diff --git a/pubspec.yaml b/pubspec.yaml
index 8af5724..d04ba6b 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -7,7 +7,7 @@
 #
 # When the minor or patch version of this is upgraded, you *must* update that
 # version constraint in pub to stay in sync with this.
-version: 0.15.2+12-dev
+version: 0.15.2+12
 
 author: "Dart Team <misc@dartlang.org>"
 homepage: http://github.com/dart-lang/barback
@@ -22,7 +22,7 @@
   Runs transforms asynchronously and in parallel when possible to maximize
   responsiveness.
 dependencies:
-  async: "^1.10.0"
+  async: ">=1.10.0 <3.0.0"
   path: ">=0.9.0 <2.0.0"
   pool: ">=1.0.0 <2.0.0"
   source_span: ">=1.0.0 <2.0.0"