Update changelog

CHANGELOG.md

@@ -4,7 +4,7 @@ All notable changes to thoth will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## \[Unreleased\]
+## [[0.1.6]](https://github.com/OpenBookPublishers/thoth/releases/tag/v0.1.6) - 2020-03-26
 ### Changed
   - Fix incompatibilities with OAPEN ONIX parser
   - Map ONIX parameter to UUID directly, instead of converting afterwards