Update gateway-js/CHANGELOG.md

Co-authored-by: Trevor Scheer <[email protected]>

Author: zionts

gateway-js/CHANGELOG.md

@@ -4,7 +4,7 @@
 
 > The changes noted within this `vNEXT` section have not been released yet.  New PRs and commits which introduce changes should include an entry in this `vNEXT` section as part of their development.  When a release is being prepared, a new header will be (manually) created below and the appropriate changes within that release will be moved into the new section.
 
-- Whenever "AccessDenied" 403 error comes from Apollo, provide a useful error message indicating how to resolve the problem
+- Whenever "AccessDenied" 403 error comes from Apollo, provide a useful error message indicating how to resolve the problem. [PR #245](https://github.com/apollographql/federation/pull/245)
 
 ## v0.21.0