Fixed changelog for MR 8501

CHANGELOG

@@ -16,6 +16,7 @@ v 7.9.0 (unreleased)
   - Allow user confirmation to be skipped for new users via API
   - Add a service to send updates to an Irker gateway (Romain Coltel)
   - Add brakeman (security scanner for Ruby on Rails)
+  - Slack username and channel options
 
 v 7.8.1
   - Fix run of custom post receive hooks
@@ -92,7 +93,6 @@ v 7.8.0
   - Improve database performance for GitLab
   - Add Asana service (Jeremy Benoist)
   - Improve project web hooks with extra data
-  - Slack username and channel options
 
 v 7.7.2
   - Update GitLab Shell to version 2.4.2 that fixes a bug when developers can push to protected branch