Add reference for realse v2 to Changelog

Author: dmnc

CHANGELOG.md

@@ -38,6 +38,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 Posterity release
 
 
-[Unreleased]: https://github.com/pda/flexihash/compare/v1.0.0...master
+[Unreleased]: https://github.com/pda/flexihash/compare/v2.0.0...master
+[2.0.0]: https://github.com/pda/flexihash/compare/v1.0.0...v2.0.0
 [1.0.0]: https://github.com/pda/flexihash/compare/v0.1.0...v1.0.0
 [0.1.0]: https://github.com/pda/flexihash/tree/v0.1.0