Update changelog for new release.

Author: jltorresm

CHANGELOG.md

@@ -5,6 +5,8 @@ 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]
+
+## [v0.3.0] - 2020-09-09
 ### Added
 - Clean json marshalling for internal configurations.
 - Improve test coverage and go docs.
@@ -37,5 +39,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Basic go module configuration, README, badges.
 
 [Unreleased]: https://github.com/jltorresm/otpgo/compare/v0.2.0...HEAD
+[v0.3.0]: https://github.com/jltorresm/otpgo/compare/v0.2.0...v0.3.0
 [v0.2.0]: https://github.com/jltorresm/otpgo/compare/v0.1.0...v0.2.0
 [v0.1.0]: https://github.com/jltorresm/otpgo/compare/5130d24...v0.1.0