Update CHANGELOG.md

Author: pluma

CHANGELOG.md

@@ -5,7 +5,9 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
-## [6.0.0]
+## [Unreleased]
+
+## [6.0.0] - 2018-01-11
 
 ### Removed