Update changelog in master.

CHANGELOG

@@ -8,6 +8,11 @@ v 6.8.0
   - Create branches via API (sponsored by O'Reilly Media)
   - Changed permission of gitlab-satellites directory not to be world accessible
+v 6.7.3
+  - Fix the merge notification email not being sent (Pierre de La Morinerie)
+  - Drop all tables before restoring a Postgres backup
+  - Remove yanked modernizr gem
+
 v 6.7.2
   - Fix upgrader script