Update CHANGELOG

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CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
-v 8.3.0 (unreleased)
-v 8.4.0 (unreleased)
-  - Fix Error 500 when doing a search in dashboard before visiting any project (Stan Hu)
-  - Implement new UI for group page
-  - Add project permissions to all project API endpoints (Stan Hu)
-
-v 8.3.1 (unreleased)
+v 8.3.1
   - Fix Error 500 when global milestones have slashes (Stan Hu)
+  - Fix Error 500 when doing a search in dashboard before visiting any project (Stan Hu)
+  - Fix LDAP identity and user retrieval when special characters are used
+  - Move Sidekiq-cron configuration to gitlab.yml
 
 v 8.3.0
-  - Add CAS support (tduehr)
   - Bump rack-attack to 4.3.1 for security fix (Stan Hu)
   - API support for starred projects for authorized user (Zeger-Jan van de Weg)
   - Add open_issues_count to project API (Stan Hu)