update changelog reference links

Author: jspaleta

CHANGELOG.md

@@ -98,7 +98,8 @@ This CHANGELOG follows the format listed [here](https://github.com/sensu-plugins
 ### Added
 - initial release
 
-[Unreleased]: https://github.com/sensu-plugins/sensu-plugins-java/compare/2.0.0...HEAD
+[Unreleased]: https://github.com/sensu-plugins/sensu-plugins-java/compare/3.0.0...HEAD
+[3.0.0]: https://github.com/sensu-plugins/sensu-plugins-java/compare/2.0.0...3.0.0
 [2.0.0]: https://github.com/sensu-plugins/sensu-plugins-java/compare/1.3.0...2.0.0
 [1.3.0]: https://github.com/sensu-plugins/sensu-plugins-java/compare/1.2.0...1.3.0
 [1.2.0]: https://github.com/sensu-plugins/sensu-plugins-java/compare/1.1.0...1.2.0