Update CHANGELOG-EE

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CHANGELOG-EE

@@ -2,6 +2,9 @@ v 8.4.0 (unreleased)
   - Add ability to create a note for user by admin
   - Fix "Commit was rejected by git hook", when max_file_size was set null in project's Git hooks
+v 8.3.1
+  - Rename "Group Statistics" to "Contribution Analytics"
+
 v 8.3.0
   - License information can now be retrieved via the API
   - Show Kerberos clone url when Kerberos enabled and url different than HTTP url (Borja Aparicio)