Update Changelog

CHANGELOG.md

@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+
+## [v0.3.1]
+- Fixed typo in variable name [[#15](https://github.com/xmidt-org/codex-db/pull/15)]
 - Fix metric cardinality [[#17](https://github.com/xmidt-org/codex-db/pull/17)]
 
 ## [v0.3.0]
@@ -27,7 +30,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ## [v0.1.0]
 - Initial creation, moved from: https://github.com/xmidt-org/codex-deploy
 
-[Unreleased]: https://github.com/xmidt-org/codex-db/compare/v0.3.0..HEAD
+[Unreleased]: https://github.com/xmidt-org/codex-db/compare/v0.3.1..HEAD
+[v0.3.1]: https://github.com/xmidt-org/codex-db/compare/v0.3.0..v0.3.1
 [v0.3.0]: https://github.com/xmidt-org/codex-db/compare/v0.2.0..v0.3.0
 [v0.2.0]: https://github.com/xmidt-org/codex-db/compare/0.1.2...v0.2.0
 [v0.1.2]: https://github.com/xmidt-org/codex-db/compare/0.1.1...v0.1.2