Update CHANGELOG.md for 9.1.8

[ci skip]

CHANGELOG.md

@@ -521,6 +521,13 @@ entry.
 - Fix preemptive scroll bar on user activity calendar.
 - Pipeline chat notifications convert seconds to minutes and hours.
+## 9.1.8 (2017-07-19)
+
+- Improve support for external issue references. !12485
+- Renders 404 if given project is not readable by the user on Todos dashboard.
+- Fix incorrect project authorizations.
+- Remove uploads/appearance symlink. A leftover from a previous migration.
+
 ## 9.1.7 (2017-06-07)
 - No changes.