Update CHANGELOG.md

Author: f3ath

CHANGELOG.md

@@ -5,6 +5,8 @@ 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).
 
 ## [Unreleased]
+### Added
+- Filtering support for collections ([#97](https://github.com/f3ath/json-api-dart/pull/97))
 
 ## [4.1.0] - 2020-05-28
 ### Changed