Bump up Gerrit version to 3.1.6

Change-Id: Ia9a627817b57d09b4d364a6f7911e4393f4f009c
diff --git a/common.env b/common.env
index d078757..0c3f973 100644
--- a/common.env
+++ b/common.env
@@ -5,7 +5,7 @@
 
 # Gerrit version
 GERRIT_VERSION=3.1
-GERRIT_PATCH=5
+GERRIT_PATCH=6
 GERRIT_BRANCH=stable-$(GERRIT_VERSION)
 
 # Gerrit CI