Update CHANGELOG.md

Author: biow0lf

CHANGELOG.md

@@ -16,6 +16,7 @@ Misc:
 
 - [#2021](https://github.com/rails-api/active_model_serializers/pull/2021) Make test attributes explicit. Tests have Model#associations. (@bf4)
 - [#1981](https://github.com/rails-api/active_model_serializers/pull/1981) Fix relationship link documentation. (@groyoh)
+- [#2039](https://github.com/rails-api/active_model_serializers/pull/2039) Documentation fixes. (@biow0lf)
 
 ### [v0.10.4 (2017-01-06)](https://github.com/rails-api/active_model_serializers/compare/v0.10.3...v0.10.4)