fix: changelog for v4

Author: simllll

CHANGELOG.md

@@ -3,6 +3,8 @@
 All notable changes to this project will be documented in this file. See [standard-version](https://github.com/conventional-changelog/standard-version) for commit guidelines.
 
 ## [6.0.0](https://github.com/hokify/agenda/compare/v5.0.1...v6.0.0) (2021-08-27)
+
+### ⚠ BREAKING CHANGES
 * Upgrade to mongo driver 4
 
 ### [5.0.1](https://github.com/hokify/agenda/compare/v5.0.0...v5.0.1) (2021-02-12)