message: Remove duplicate line from CHANGELOG.
diff: @@ -5,9 +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
  -
  -- [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.
  +<!--## Unreleased-->
  ## [2.0.0] - 2017-04-14
  