Updated changelog for v0.3.1

I forgot to add an unreleased changelog entry for the CCM fixes, so I
added that here.

Author: jnschaeffer

CHANGELOG.md

@@ -10,6 +10,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 <!--- end unreleased changes --->
 <!--- remember to add diff link to footer --->
 
+## [v0.3.1] (2019-12-17)
+
+### Fixed
+
+* CCM now sets backend nodes correctly when adding ports on LoadBalancer service update.
+
 ## [v0.3.0] (2019-11-06)
 
 ### Added