Update CHANGELOG

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CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 v 8.4.0 (unreleased)
-  - Fix Error 500 when doing a search in dashboard before visiting any project (Stan Hu)
   - Implement new UI for group page
   - Implement search inside emoji picker
   - Add project permissions to all project API endpoints (Stan Hu)
@@ -12,6 +11,9 @@ v 8.4.0 (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
   - Bump rack-attack to 4.3.1 for security fix (Stan Hu)