Add changelog for PR #810

Author: scaredcat

CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [1.3.1] unreleased
 ### Fixed
 * #812: Reverts #643 pass wrong request object to authenticate function.
+* Fix concurrency issue with refresh token requests (#[810](https://github.com/jazzband/django-oauth-toolkit/pull/810))
 
 ## [1.3.0] 2020-03-02