Build zookeeper-refdb against gerrit stable-3.6

Bug: Issue 15831
Change-Id: Idd96ed8893a166e2123272d951d0d3b3fc6221e0
diff --git a/jenkins/gerrit-bazel-plugin-zookeeper-refdb.yaml b/jenkins/gerrit-bazel-plugin-zookeeper-refdb.yaml
index aac4b8b..d8028aa 100644
--- a/jenkins/gerrit-bazel-plugin-zookeeper-refdb.yaml
+++ b/jenkins/gerrit-bazel-plugin-zookeeper-refdb.yaml
@@ -5,6 +5,7 @@
           targets: "plugins/{name}:{name} plugins/{name}:{name}-zk-3.5"
           branch:
             - master
+            - stable-3.6
             - stable-3.5
             - stable-3.4
             - stable-3.3