Set GERRIT_VERSION to stable-3.11

Change-Id: I3e587dcf0739c87d0b3e01f32760409c378ab98c

src/test/docker/gerrit/Dockerfile

diff --git a/src/test/docker/gerrit/Dockerfile b/src/test/docker/gerrit/Dockerfile
index aeac272..74ba1a2 100644
--- a/src/test/docker/gerrit/Dockerfile
+++ b/src/test/docker/gerrit/Dockerfile
@@ -10,7 +10,7 @@
     gettext \
     && yum -y clean all
 
-ENV GERRIT_VERSION master
+ENV GERRIT_VERSION stable-3.11
 
 # Add gerrit user
 RUN adduser -p -m --uid 1000 gerrit --home-dir /home/gerrit