Prepare 1.6.8 release

Author: MarioBlazek

doc/CHANGELOG.md

@@ -6,6 +6,11 @@ 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/).
 
+## [1.6.8] - 2019-04-26
+### Added
+- A bit more looser coupling to `doctrine/orm` version
+- Documented Google invisible captcha - tnx @ludwig031
+
 ## [1.6.7] - 2019-04-16
 ### Fixed
 - Legacy controller should also handle captcha errors