[CHANGELOG.md] Document latest changes

Author: Jeehut

CHANGELOG.md

@@ -7,7 +7,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 ### Added
 - None.
 ### Changed
-- None.
+- Make some fields of the `JsonApi` protocol optional by providing default implementation.
 ### Deprecated
 - None.
 ### Removed