update develop changelog with latest release

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 
 ## [Unreleased]
+
+## [2.2.2] - 2020-12-22
 ### Added
 - Mouseover titles for emojis in reaction picker
 - Support to input emoji into the search box in reaction picker