Update changelog for 7.8.4.

CHANGELOG

@@ -52,6 +52,12 @@ v 7.9.0 (unreleased)
   - Starred projects page at dashboard
   - Make email display name configurable
   - Improve json validation in hook data
+v 7.8.4
+  - Fix issue_tracker_id substitution in custom issue trackers
+  - Fix path and name duplication in namespaces
+
+v 7.8.3
+  - Bump version of gitlab_git fixing annotated tags without message
 v 7.8.2
   - Fix service migration issue when upgrading from versions prior to 7.3