Update CHANGELOG

Author: thrawn01

CHANGELOG

@@ -4,6 +4,13 @@ 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/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2.2.0] - 2019-07-09
+### Added
+* Added `SetLogger()` to pass in a logrus entry for logging peer errors
+* Added `DeregisterGroup()` to remove an existing group cache
+### Changes
+* Fixed race condition in `Remove()`
+
 ## [2.1.0] - 2019-06-10
 ### Changes
 * `Get()` now returns immediately when context is done during a groupcache peer