Prepare to publish 0.12.4 (#97)

diff --git a/pubspec.yaml b/pubspec.yaml
index 8a00849..5250a12 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: matcher
-version: 0.12.3+1
+version: 0.12.4
 
 description: Support for specifying test expectations
 author: Dart Team <misc@dartlang.org>
@@ -13,3 +13,6 @@
 
 dev_dependencies:
   test: '>=0.12.0 <2.0.0'
+
+dependency_overrides:
+  test: ^1.3.0