Add changelog.

Author: beauby

CHANGELOG.md

@@ -16,6 +16,7 @@ Breaking changes:
 
 Features:
 
+- [#1403](https://github.com/rails-api/active_model_serializers/pull/1403) Add support for if/unless on attributes/associations (@beauby)
 - [#1336](https://github.com/rails-api/active_model_serializers/pull/1336) Added support for Grape >= 0.13, < 1.0
 - [#1291](https://github.com/rails-api/active_model_serializers/pull/1291) Add logging (@maurogeorge)
 - [#1225](https://github.com/rails-api/active_model_serializers/pull/1225) Better serializer lookup, use nested serializer when it exists (@beauby)