Fix CHANGELOG reference

Author: colinodell

CHANGELOG.md

@@ -18,5 +18,5 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 Initial release!
 
 [unreleased]: https://github.com/thephpleague/commonmark-ext-external-link/compare/v1.0.0-beta1...HEAD
-[v1.0.0-beta1]: https://github.com/thephpleague/commonmark-ext-external-link/compare/v0.1.0...v1.0.0-beta1
+[1.0.0-beta1]: https://github.com/thephpleague/commonmark-ext-external-link/compare/v0.1.0...v1.0.0-beta1
 [0.1.0]: https://github.com/thephpleague/commonmark-ext-external-link/commits/v0.1.0