Build the oauth plugin for stable-3.1

Change-Id: I8228bd9a36e6b7ba83a446fd01e3457754a216a5
diff --git a/jenkins/gerrit-bazel-plugin-oauth.yaml b/jenkins/gerrit-bazel-plugin-oauth.yaml
index d619a2d..699fadc 100644
--- a/jenkins/gerrit-bazel-plugin-oauth.yaml
+++ b/jenkins/gerrit-bazel-plugin-oauth.yaml
@@ -7,4 +7,9 @@
             - stable-2.15
             - stable-2.16
             - stable-3.0
+      - 'plugin-{name}-bazel-{branch}-{gerrit-branch}':
+          branch:
             - master
+          gerrit-branch:
+            - master
+            - stable-3.1