Build simple-submit-rules for stable-3.0

Change-Id: I7616fa18a4d4798efbe9815b78d7ed2e55eed86d
diff --git a/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml b/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml
index 479dd86..6580ece 100644
--- a/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml
+++ b/jenkins/gerrit-bazel-plugin-simple-submit-rules.yaml
@@ -4,4 +4,5 @@
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master
+            - stable-3.0
             - stable-2.16