Fix CHANGELOG

Author: pluma

CHANGELOG.md

@@ -1912,6 +1912,7 @@ For a detailed list of changes between pre-release versions of v7 see the
 
   Graph methods now only return the relevant part of the response body.
 
+[unreleased]: https://github.com/arangodb/arangojs/compare/v9.0.0-preview.4...HEAD
 [9.0.0-preview.4]: https://github.com/arangodb/arangojs/compare/v9.0.0-preview.3...v9.0.0-preview.4
 [9.0.0-preview.3]: https://github.com/arangodb/arangojs/compare/v9.0.0-preview.2...v9.0.0-preview.3
 [9.0.0-preview.2]: https://github.com/arangodb/arangojs/compare/v9.0.0-preview.1...v9.0.0-preview.2