Update CHANGELOG.md for 8.13.12

[ci skip]

CHANGELOG.md

@@ -563,6 +563,14 @@ entry.
 - Fix "Without projects" filter. !6611 (Ben Bodenmiller)
 - Fix 404 when visit /projects page
 
+## 8.13.12 (2017-01-21)
+
+- Ensure export files are removed after a namespace is deleted.
+- Don't allow project guests to subscribe to merge requests through the API. (Robert Schilling)
+- Prevent users from creating notes on resources they can't access.
+- Prevent users from deleting system deploy keys via the project deploy key API.
+- Upgrade omniauth gem to 1.3.2.
+
 ## 8.13.11 (2017-01-10)
 
 - Update the gitlab-markup gem to the version 1.5.1. !8509