Update CHANGELOG.md for 11.3.4

[ci skip]

CHANGELOG.md

@@ -2,6 +2,15 @@
 documentation](doc/development/changelog.md) for instructions on adding your own
 entry.
 
+## 11.3.4 (2018-10-05)
+
+### Security (3 changes)
+
+- Filter user sensitive data from discussions JSON. !2537
+- Properly filter private references from system notes.
+- Markdown API no longer displays confidential title references unless authorized.
+
+
 ## 11.3.3 (2018-10-04)
 
 - No changes.