Add stable-2.13 branch to server-config

Change-Id: I6adfaaf352cff95bc070d7243ce3fd074bedee1e
diff --git a/jenkins/gerrit-buck-bazel-plugin-server-config.yaml b/jenkins/gerrit-buck-bazel-plugin-server-config.yaml
index 9be7bae..2aa0dee 100644
--- a/jenkins/gerrit-buck-bazel-plugin-server-config.yaml
+++ b/jenkins/gerrit-buck-bazel-plugin-server-config.yaml
@@ -1,6 +1,9 @@
 - project:
     name: server-config
     jobs:
+      - 'plugin-{name}-{branch}':
+          branch:
+            - stable-2.13
       - 'plugin-{name}-bazel-{branch}':
           branch:
             - master