Add missing changelog reflink for @andykenward

CHANGELOG.md

@@ -1875,6 +1875,7 @@ Not usable for others, only stubs of classes etc. - [@orta]
 [@aghassi]: https://github.com/aghassi
 [@ahobson]: https://github.com/ahobson
 [@alexandermendes]: https://github.com/alexandermendes
+[@andykenward]: https://github.com/andykenward
 [@ashfurrow]: https://github.com/ashfurrow
 [@awgeorge]: https://github.com/awgeorge
 [@azz]: https://github.com/azz