Update CHANGELOG.md for 8.13.8

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CHANGELOG.md

 Please view this file on the master branch, on stable branches it's out of date.
 
+## 8.13.8 (2016-12-02)
+
+- Pass tag SHA to post-receive hook when tag is created via UI. !7700
+- Validate state param when filtering issuables.
+
 ## 8.13.7 (2016-11-28)
 
 - fixes 500 error on project show when user is not logged in and project is still empty. !7376

changelogs/unreleased/24813-project-members-with-developer-access-can-no-longer-create-tags.yml

----
-title: Pass tag SHA to post-receive hook when tag is created via UI
-merge_request: 7700
-author:

changelogs/unreleased/validate-state-param-when-filtering-issuables.yml

----
-title: Validate state param when filtering issuables
-merge_request:
-author: