changelog: Add entry for windows newline bugfix

Author: Bjwebb

CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - All code has had black and isort applied. These have been added to Travis.
 
+## Fixed
+
+- Remove extra lines in CSVs under Windows https://github.com/OpenDataServices/flatten-tool/pull/350
+
 ## [0.11.0] - 2020-02-21
 
 ### Added