Use Gerrit 2.16.19 in Dockerfile

Change-Id: I4bd17387d513f99573b0ce982dc26afa24b6ed30

src/test/docker/gerrit/Dockerfile

diff --git a/src/test/docker/gerrit/Dockerfile b/src/test/docker/gerrit/Dockerfile
index 2d2aed0..0328827 100644
--- a/src/test/docker/gerrit/Dockerfile
+++ b/src/test/docker/gerrit/Dockerfile
@@ -1,4 +1,4 @@
-FROM gerritcodereview/gerrit:2.16.18
+FROM gerritcodereview/gerrit:2.16.19
 
 ENV GERRIT_BRANCH=stable-2.16