add date to changelog

Author: LauLauThom

CHANGELOG.md

@@ -3,7 +3,7 @@ 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/).  
 
-## [1.6.1] - SOON
+## [1.6.1] - 2020-08-20
 ### Added
 - support mask for matchTemplates and findMatches as in cv2.matchTemplates with method 0 or 3
 - notebook tutorial with mask