req.body is not a function + wrong mapping

1. TypeError: req.body is not a function
   ext-track-labels-trackingWebhook
   at /workspace/lib/index.js:27:60

in the webhook function need to change req.body() to req.body (notice #2 req.body.data)

2. the mapping to req.body should be changed to req.body.data to match the schema mapping
   so change req.body() to req.body.data