Update CHANGELOG

Author: bouwew

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ## Ongoing
 
-- Code optimizations via PR [#837](https://github.com/plugwise/python-plugwise/pull/837), [#838](https://github.com/plugwise/python-plugwise/pull/838)
+- Code optimizations via PR [#837](https://github.com/plugwise/python-plugwise/pull/837), [#838](https://github.com/plugwise/python-plugwise/pull/838), [#839](https://github.com/plugwise/python-plugwise/pull/839)
 
 ## v1.11.0