updated changelog with the last version and release date

Author: oscarotero

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/) 
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
-## UNRELEASED
+## [0.4.0] - 2017-09-21
 
 ### Changed
 
@@ -31,5 +31,6 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 First version
 
+[0.4.0]: https://github.com/middlewares/geolocation/compare/v0.3.0...v0.4.0
 [0.3.0]: https://github.com/middlewares/geolocation/compare/v0.2.0...v0.3.0
 [0.2.0]: https://github.com/middlewares/geolocation/compare/v0.1.0...v0.2.0