fix unittest dependency

R=nweiz@google.com

Review URL: https://codereview.chromium.org//884553002
diff --git a/pubspec.yaml b/pubspec.yaml
index 57f34f5..d6d35a0 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,9 +1,9 @@
 name: metatest
-version: 0.1.1
+version: 0.1.2-dev
 author: Dart Team <misc@dartlang.org>
 description: A package for testing Dart test frameworks.
 homepage: https://github.com/dart-lang/metatest
 environment:
   sdk: '>=1.0.0 <2.0.0'
 dependencies:
-  unittest: '>=0.11.0 <=0.12.0'
+  unittest: '>=0.11.0 <0.13.0'