Update CHANGELOG.md for 9.1.9

[ci skip]

CHANGELOG.md

@@ -529,6 +529,10 @@ entry.
 - Fix preemptive scroll bar on user activity calendar.
 - Pipeline chat notifications convert seconds to minutes and hours.
 
+## 9.1.9 (2017-07-20)
+
+- Fix an infinite loop when handling user-supplied regular expressions.
+
 ## 9.1.8 (2017-07-19)
 
 - Improve support for external issue references. !12485