Prepare for 0.13.1 release

R=jakemac@google.com

Review URL: https://codereview.chromium.org//554813002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/observe@39995 260f80e4-7a28-3924-810f-c04153c831b5
2 files changed
tree: f718bcf7e11b9f5198d5a3e53d8762fe51b9ed5e
  1. lib/
  2. test/
  3. AUTHORS
  4. CHANGELOG.md
  5. LICENSE
  6. PATENTS
  7. pubspec.yaml