Build reviewassistant on 3.0 and 3.1 branch

Change-Id: Ide41812c87d8f478fa0c77ac9e42af026ad85e81
diff --git a/jenkins/gerrit-bazel-plugin-reviewassistant.yaml b/jenkins/gerrit-bazel-plugin-reviewassistant.yaml
index 4c3701e..74a5e50 100644
--- a/jenkins/gerrit-bazel-plugin-reviewassistant.yaml
+++ b/jenkins/gerrit-bazel-plugin-reviewassistant.yaml
@@ -4,4 +4,6 @@
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master
+            - stable-3.1
+            - stable-3.0
             - stable-2.16