Update CHANGELOG.md

Author: miguelalonsojr

com.unity.ml-agents/CHANGELOG.md

@@ -6,7 +6,7 @@ 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).
 
-## [2.2.0] - 2022-01-14
+## [2.2.0-exp.1] - 2022-01-14
 ### Major Changes
 
 #### com.unity.ml-agents / com.unity.ml-agents.extensions (C#)