update changelog

CHANGELOG-EE

 Please view this file on the master branch, on stable branches it's out of date.
-v 8.6.0
-  - [Elasticsearch] Removing repository and wiki index after removing project
-
-v 8.5.0
 v 8.6.0 (unreleased)
   - Improve weight filter for issues
   - [Elastic] Add elastic checker to gitlab:check
   - [Elastic] Added UPDATE_INDEX option to rake task
+  - [Elasticsearch] Removing repository and wiki index after removing project
 
 v 8.5.1
   - Fix adding pages domain to projects in groups