Use Gerrit 2.16.16 in Dockerfile

Change-Id: I4c57fe0db1ace368d97fdba4aa5d2a092fc4fd19
diff --git a/src/test/docker/gerrit/Dockerfile b/src/test/docker/gerrit/Dockerfile
index 4664ba0..9b2083d 100644
--- a/src/test/docker/gerrit/Dockerfile
+++ b/src/test/docker/gerrit/Dockerfile
@@ -1,4 +1,4 @@
-FROM gerritcodereview/gerrit:2.16.15
+FROM gerritcodereview/gerrit:2.16.16
 
 ENV GERRIT_BRANCH=stable-2.16