Add PR reference

Author: Sephster

CHANGELOG.md

@@ -9,7 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ## [7.1.1] - released 2018-05-21
 
 ### Fixed
-- No longer set a WWW-Authenticate header for invalid clients if the client did not send an Authorization header in the original request
+- No longer set a WWW-Authenticate header for invalid clients if the client did not send an Authorization header in the original request (PR #902)
 
 ## [7.1.0] - released 2018-04-22