added release date

Author: mariodavid

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](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
-## [0.4.0] - Unreleased
+## [0.4.0] - 2018-07-13
 
 ### Change
 - show sender attribute in show-message screen