update Changie header template (KeepAChangelog v1.1.0)

Author: llaville

.changes/2.x/header.tpl.md

@@ -3,6 +3,6 @@
 
 All notable changes to this project v2 release series will be documented in this file.
 
-The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html),
 and is generated by [Changie](https://github.com/miniscruff/changie).