Update version in changelog

Author: athinab

CHANGELOG.md

@@ -5,7 +5,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 
-## [Unreleased]
+## [v2.1.0](https://github.com/rciam/simplesamlphp-module-themevanilla/compare/v2.0.0...v2.1.0) - 2018-10-18
 
 ### Added
 - Add banner and an extra view for cookies options