Add stable-2.12 branch to the wip plugin

Change-Id: I965526b26074aef9d0e9e51796ec00269bff0e9c
diff --git a/jenkins/gerrit-buck-plugin-wip.yaml b/jenkins/gerrit-buck-plugin-wip.yaml
index 2527b1c..02cea74 100644
--- a/jenkins/gerrit-buck-plugin-wip.yaml
+++ b/jenkins/gerrit-buck-plugin-wip.yaml
@@ -2,6 +2,7 @@
     name: wip
     branch:
       - master
+      - stable-2.12
     jobs:
       - 'plugin-{name}-{branch}'