Add a missing CHANGELOG item

[ci skip]
Signed-off-by: Rémy Coutable <remy@rymai.me>

CHANGELOG.md

@@ -3,6 +3,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 ## 8.13.6 (2016-11-17)
 
 - Omniauth auto link LDAP user falls back to find by DN when user cannot be found by UID. !7002
+- Fix Milestone dropdown not stay selected for `Upcoming` and `No Milestone` option. !7117
 - Fix no "Register" tab if ldap auth is enabled (#24038). !7274 (Luc Didry)
 - Fix cache for commit status in commits list to respect branches. !7372
 - Fix issue causing Labels not to appear in sidebar on MR page. !7416 (Alex Sanford)