Build zookeeper-refdb plugin on stable-3.3

Change-Id: I2bf3dffee7ac34be281b427d6357bd5416f22097
diff --git a/jenkins/gerrit-bazel-plugin-zookeeper-refdb.yaml b/jenkins/gerrit-bazel-plugin-zookeeper-refdb.yaml
index d9fdd5e..48a9558 100644
--- a/jenkins/gerrit-bazel-plugin-zookeeper-refdb.yaml
+++ b/jenkins/gerrit-bazel-plugin-zookeeper-refdb.yaml
@@ -4,6 +4,7 @@
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master
+            - stable-3.3
             - stable-3.1
             - stable-3.0
       - 'plugin-{name}-bazel-{branch}':