Update the changelog

Author: stakx

CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to this project will be documented in this file.
 The format is loosely based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 
+## Unreleased
+
+#### Fixed
+
+* Regression since 4.14.0: setting nested non-overridable properties via `Mock.Of` (@mariotee, #1039)
+
+
 ## 4.14.5 (2020-07-01)
 
 #### Fixed