Base Unreleased section of CHANGELOG on v4.0.0

Author: aaron-lane

CHANGELOG.md

@@ -143,7 +143,7 @@ Extending the adopted spec, each change should have a link to its corresponding
 
 * Initial release of module.
 
-[Unreleased]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v3.0.0...HEAD
+[Unreleased]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v4.0.0...HEAD
 [v4.0.0]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v3.0.0...v4.0.0
 [v3.0.0]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v2.1.0...v3.0.0
 [v2.1.0]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v2.0.1...v2.1.0