Build automerger plugin on recent branches

Change-Id: I9b94826308bdecf66443288b30753ad2036ef8c2
diff --git a/jenkins/gerrit-bazel-plugin-automerger.yaml b/jenkins/gerrit-bazel-plugin-automerger.yaml
index a09f6bc..c21ab9f 100644
--- a/jenkins/gerrit-bazel-plugin-automerger.yaml
+++ b/jenkins/gerrit-bazel-plugin-automerger.yaml
@@ -6,6 +6,9 @@
             - master
           gerrit-branch:
             - master
+            - stable-3.3
       - 'plugin-{name}-bazel-{branch}':
           branch:
+            - stable-3.2
+            - stable-3.1
             - stable-2.16