Update CHANGELOG.

Author: jaredhanson

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.6.1] - 2021-09-24
+### Fixed
+- Error in cases where the authorization server returns a successful access
+token response which is missing an `access_token` parameter.
+
 ## [1.6.0] - 2021-07-01
 ### Added