Add entry in CHANGELOG for #1560

Author: Yohan Robert

CHANGELOG.md

@@ -31,6 +31,7 @@ Fixes:
 - [#1488](https://github.com/rails-api/active_model_serializers/pull/1488) Require ActiveSupport's string inflections (@nate00)
 
 Misc:
+- [#1560](https://github.com/rails-api/active_model_serializers/pull/1560) Update rubocop and address its warnings. (@bf4 @groyoh)
 - [#1545](https://github.com/rails-api/active_model_serializers/pull/1545) Document how to pass arbitrary options to the
   serializer (@CodedBeardedSignedTaylor)
 - [#1496](https://github.com/rails-api/active_model_serializers/pull/1496) Run all branches against JRuby on CI (@nadavshatz)