Build webhooks stable-2.13 with buck

The webhooks stable-2.13 branch is build with buck, not bazel.

Change-Id: I64b235e24b95663bcb11269a7d092d93e451767e
diff --git a/jenkins/gerrit-bazel-plugin-webhooks.yaml b/jenkins/gerrit-bazel-plugin-webhooks.yaml
index ea93df9..b55ed5a 100644
--- a/jenkins/gerrit-bazel-plugin-webhooks.yaml
+++ b/jenkins/gerrit-bazel-plugin-webhooks.yaml
@@ -1,10 +1,11 @@
 - project:
     name: webhooks
     jobs:
+      - 'plugin-{name}-{branch}':
+          branch:
+            - stable-2.13
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master
             - stable-2.15
             - stable-2.14
-            - stable-2.13
-