Use Gerrit 3.0.8 in Dockerfile

Change-Id: Ieb83d9b3590ba1a6dacefb3ba01ceee70367dfb3
diff --git a/src/test/docker/gerrit/Dockerfile b/src/test/docker/gerrit/Dockerfile
index f320687..b5c7b31 100644
--- a/src/test/docker/gerrit/Dockerfile
+++ b/src/test/docker/gerrit/Dockerfile
@@ -1,4 +1,4 @@
-FROM gerritcodereview/gerrit:3.0.7
+FROM gerritcodereview/gerrit:3.0.8
 
 ENV GERRIT_BRANCH=stable-3.0