Update changelog

Author: JP Wright

CHANGELOG.md

@@ -5,6 +5,10 @@ This project adheres to [Semantic Versioning](http://semver.org/) starting from
 
 ### Merged, but not yet released
 > All recent changes are published
+> #### Fixed
+> - If an entry was of a content type not known to the `Client`, the SDK would enter an infinite loop.
+> #### Changed
+> - `MixedMappedArrayResponse` is now called `HeterogeneousMappedArrayResponse`
 ---
 
 ## Table of contents