Update CHANGELOG-EE.md for 11.5.11-ee

[ci skip]

CHANGELOG-EE.md

@@ -690,6 +690,13 @@ Please view this file on the master branch, on stable branches it's out of date.
 - Use new information-o icon for Security Dashboard.
 
 
+## 11.5.11 (2019-04-23)
+
+### Security (1 change)
+
+- Respect group membership lock when importing a member from another group.
+
+
 ## 11.5.8 (2019-01-28)
 
 ### Security (6 changes)