Tweak the concurrency settings a bit and release.

R=kevmoo@google.com

Review URL: https://codereview.chromium.org//1214573002.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index e72a548..444d460 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 0.12.4
+## 0.12.3+3
 
 * Limit the number of test suites loaded at once. This helps ensure that the
   test runner won't run out of memory when running many test suites that each
diff --git a/lib/src/runner/engine.dart b/lib/src/runner/engine.dart
index 208d4f7..c570d4a 100644
--- a/lib/src/runner/engine.dart
+++ b/lib/src/runner/engine.dart
@@ -144,7 +144,7 @@
   Engine({int concurrency, int maxSuites})
       : _runPool = new Pool(concurrency == null ? 1 : concurrency),
         _loadPool = new Pool(maxSuites == null
-            ? (concurrency == null ? 4 : concurrency * 4)
+            ? (concurrency == null ? 2 : concurrency * 2)
             : maxSuites) {
     _group.future.then((_) {
       if (_closedBeforeDone == null) _closedBeforeDone = false;
diff --git a/pubspec.yaml b/pubspec.yaml
index 9dc7aaf..d292fd2 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: test
-version: 0.12.4-dev
+version: 0.12.3+3
 author: Dart Team <misc@dartlang.org>
 description: A library for writing dart unit tests.
 homepage: https://github.com/dart-lang/test
@@ -8,9 +8,7 @@
 dependencies:
   analyzer: '>=0.23.0 <0.26.0'
   args: '>=0.12.1 <0.14.0'
-  # TODO(nweiz): Use a hosted dependency once async 0.13.2 is published. Don't
-  # publish this with a git dependency.
-  async: {git: git://github.com/dart-lang/async}
+  async: '^1.2.0'
   barback: '>=0.14.0 <0.16.0'
   crypto: '^0.9.0'
   glob: '^1.0.0'