Bump version to publish 0.13.0.

R=terry@google.com

Review URL: https://codereview.chromium.org//1912463002 .
diff --git a/pubspec.yaml b/pubspec.yaml
index 8a9507e..06690f5 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,6 @@
 name: csslib
-version: 0.13.0-dev
-author: Polymer.dart Team <web-ui-dev@dartlang.org>
+version: 0.13.0
+author: Dart Team <misc@dartlang.org>
 description: A library for parsing CSS.
 homepage: https://github.com/dart-lang/csslib
 environment: