Build owners plugin on stable-3.1

Change-Id: Ie29c55726f8d1fbfb59be87d36c465e744966388
diff --git a/jenkins/gerrit-bazel-plugin-owners.yaml b/jenkins/gerrit-bazel-plugin-owners.yaml
index df71b78..096afd9 100644
--- a/jenkins/gerrit-bazel-plugin-owners.yaml
+++ b/jenkins/gerrit-bazel-plugin-owners.yaml
@@ -56,5 +56,6 @@
           targets: 'plugins/owners plugins/owners-autoassign'
           branch:
             - master
+            - stable-3.1
             - stable-3.0
             - stable-2.16