Release 0.12.20+3. (#565)

diff --git a/pubspec.yaml b/pubspec.yaml
index dd0e98a..82debcd 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: test
-version: 0.12.20+2
+version: 0.12.20+3
 author: Dart Team <misc@dartlang.org>
 description: A library for writing dart unit tests.
 homepage: https://github.com/dart-lang/test