Update changelog

Author: olgabrani

CHANGELOG.md

@@ -4,7 +4,7 @@ All notable changes to this project will be documented in this file.
 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]
+## [v3.0.0](https://github.com/rciam/simplesamlphp-module-themevanilla/compare/v2.3.1...v3.0.0) - 2019-09-20
 
 ### Added
 - Add languages (Xhosa, Zulu, Afrikaans).