Build simple-submit-rules plugin on stable-3.4 branch

Change-Id: I5166f8d04dc435021e3b5c74c3f9228d930ba48e
diff --git a/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml b/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml
index d2bb0cc..7890a4b 100644
--- a/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml
+++ b/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml
@@ -11,4 +11,5 @@
             - master
           gerrit-branch:
             - master
+            - stable-3.4
             - stable-3.3