Update CHANGELOG-EE.md for 13.1.8-ee

[ci skip]

CHANGELOG-EE.md

@@ -391,6 +391,10 @@ Please view this file on the master branch, on stable branches it's out of date.
 - Resolve duplicate use of shorcuts-tree. !36732
+## 13.1.8 (2020-08-18)
+
+- No changes.
+
 ## 13.1.7 (2020-08-17)
 - No changes.