Update CHANGELOG.md

Author: Art4

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://github.com/kbsali/php-redmine-api/compare/v2.1.0...v2.x)
 
+### Fixed
+
+- Allow unassign user from an issue
+
 ## [v2.1.1](https://github.com/kbsali/php-redmine-api/compare/v2.1.0...v2.1.1) - 2022-01-15
 
 ### Fixed