Update CHANGELOG.md

Updated for v2.22.0

Signed-off-by: Mark Ziegler <mark.ziegler@rakekniven.de>

CHANGELOG.md

@@ -5,7 +5,8 @@ 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).
 
 ## [Unreleased]
-### [2.22.0] - 2018-xx-xx
+
+## [2.22.0] - 2018-08-20
 - See https://github.com/nextcloud/ios/milestone/32
 
 ## [2.21.3] - 2018-06-30