Build git-refs-filter module on stable-3.1

Change-Id: Ic374c3929a9e65e9eb7506923c8077de3daede06
diff --git a/jenkins/gerrit-bazel-module-git-refs-filter.yaml b/jenkins/gerrit-bazel-module-git-refs-filter.yaml
index c6a9a10..08ac999 100644
--- a/jenkins/gerrit-bazel-module-git-refs-filter.yaml
+++ b/jenkins/gerrit-bazel-module-git-refs-filter.yaml
@@ -4,5 +4,6 @@
       - 'module-{name}-bazel-{branch}':
           branch:
             - master
+            - stable-3.1
             - stable-3.0
             - stable-2.16