Merge branch 'stable-3.0'

* stable-3.0:
  Prevent automatic upgrade of Gerrit package

Change-Id: I3ef1fda2b3e3a929246d0e3ae61b6883c6a38222
diff --git a/ubuntu/18/Dockerfile b/ubuntu/18/Dockerfile
index 5532f2f..f945529 100644
--- a/ubuntu/18/Dockerfile
+++ b/ubuntu/18/Dockerfile
@@ -17,6 +17,7 @@
 # (pre-trans Gerrit script needs to have access to the Java command)
 RUN apt-get -y install openjdk-8-jdk
 RUN apt-get -y install gerrit=3.1.3-1 && \
+    apt-mark hold gerrit && \
     /entrypoint.sh init && \
     rm -f /var/gerrit/etc/{ssh,secure}* && rm -Rf /var/gerrit/{static,index,logs,data,index,cache,git,db,tmp}/* && chown -R gerrit:gerrit /var/gerrit