message: update changelog for v3.0.0
diff: @@ -5,12 +5,11 @@ 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
  -<!--
  - User-visible changes must be documented here. Uncomment the Unreleased heading
  - as appropriate too.
  --->
  +<!-- Add new, unreleased changes here. -->
  +
  +## [3.0.0] - 2017-05-09
  * Add build preset support.
  * Remove Node v4 support: Node v4 is no longer in Active LTS, so as per the [Polymer Tools Node.js Support Policy](https://www.polymer-project.org/2.0/docs/tools/node-support) we will not support Node v4 going forward. Please update to Node v6 or later to continue using the latest verisons of Polymer tooling.
  