Update CHANGELOG.md for 8.13.11

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CHANGELOG.md

 Please view this file on the master branch, on stable branches it's out of date.
 
+## 8.13.11 (2017-01-10)
+
+- Update the gitlab-markup gem to the version 1.5.1. !8509
+- Updated Turbolinks to mitigate potential XSS attacks.
+
 ## 8.13.10 (2016-12-14)
 
 - API: Memoize the current_user so that sudo can work properly. !8017

changelogs/unreleased/patch-turbolinks.yml

----
-title: Updated Turbolinks to mitigate potential XSS attacks
-merge_request:
-author:

changelogs/unreleased/update-gitlab-markup-gem.yml

----
-title: Update the gitlab-markup gem to the version 1.5.1
-merge_request: 8509
-author: