fix version links in changelog

Author: dbu

CHANGELOG.md

@@ -106,7 +106,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Initial release
 
 
-[Unreleased]: https://github.com/php-http/guzzle6-adapter/compare/v2.0.0...HEAD
+[Unreleased]: https://github.com/php-http/guzzle6-adapter/compare/v2.0.1...HEAD
+[2.0.1]: https://github.com/php-http/guzzle6-adapter/compare/v2.0.0...v2.0.1
 [2.0.0]: https://github.com/php-http/guzzle6-adapter/compare/v1.1.1...v2.0.0
 [1.1.1]: https://github.com/php-http/guzzle6-adapter/compare/v1.1.0...v1.1.1
 [1.1.0]: https://github.com/php-http/guzzle6-adapter/compare/v1.0.0...v1.1.0