Return an (empty) "items" array in responses from the elastic _bulk A…

…PI (to support clients which expect it to exist)

lib/handlers/elastic_bulk.js

@@ -99,7 +99,7 @@ async function handler (req, res) {
   }
   await Promise.all(promises)
   res.header('x-elastic-product', 'Elasticsearch')
-  return res.code(200).send('{"took":0, "errors": false }')
+  return res.code(200).send('{"took":0, "errors": false, "items": [] }')
 }
 
 module.exports = handler