fix: correct type for CreateNotificationBody.collapse_id (#56)
fix: correct type for CreateNotificationBody.collapse_id (#56)

As seen in OneSignal's [API docs](https://documentation.onesignal.com/reference/create-notification), `collapse_id` parameter on the `https://onesignal.com/api/v1/notifications` endpoint is a `string`, not a `number`.
KolektifLabs/onesignal-node