Update CHANGELOG for 7.12.1

CHANGELOG

@@ -28,6 +28,15 @@ v 7.13.0 (unreleased)
   - Reporter role can manage issue tracker now: edit any issue, set assignee or milestone and manage labels
   - Better performance for pages with events list, issues list and commits list
 
+v 7.12.1
+  - Fix error when deleting a user who has projects (Stan Hu)
+  - Fix post-receive errors on a push when an external issue tracker is configured (Stan Hu)
+  - Add SAML to list of social_provider (Matt Firtion)
+  - Fix merge requests API scope to keep compatibility in 7.12.x patch release (Dmitriy Zaporozhets)
+  - Fix closed merge request scope at milestone page (Dmitriy Zaporozhets)
+  - Revert merge request states renaming 
+  - Fix hooks for web based events with external issue references (Daniel Gerhardt)
+
 v 7.12.0
   - Fix Error 500 when one user attempts to access a personal, internal snippet (Stan Hu)
   - Disable changing of target branch in new merge request page when a branch has already been specified (Stan Hu)