message: Un-comment out the Unreleased header in CHANGELOG
diff: @@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
  The format is based on [Keep a Changelog](http://keepachangelog.com/)
  and this project adheres to [Semantic Versioning](http://semver.org/).
  -<!--## Unreleased-->
  +## Unreleased
  <!-- List New Changes Here -->
  * [BREAKING] Dropped support for node v4, added support for node v8. See our [node version support policy](https://www.polymer-project.org/2.0/docs/tools/node-support) for details.
  