Bump to Gerrit v2.13.11 for macOS intaller

Change-Id: I0e1f444864bdf2f9724eb05336ce5d2fd0301ff1
diff --git a/macOS/Makefile b/macOS/Makefile
index edb1e08..d6b6cfe 100644
--- a/macOS/Makefile
+++ b/macOS/Makefile
@@ -1,4 +1,4 @@
-VERSION := 2.13.9
+VERSION := 2.13.11
 
 all: server