notifyCFNThatUploadSucceeded (responseData) {
    return notifyCFN.ofSuccess({ event: this.event, context: this.context, responseData })
  }
Uses the cfn-response library to notify CloudFormation that this custom resource is done with the task it was
invoked to do. This could be the response to a create / update request (which would upload files from S3) or a
delete request (which would delete files from S3).

@param {Object} responseData extra information about the processing for CFN; must be an object
@param {Object} event the CFN request object that kicked off this custom resource
@param {Object} context lambda function context

@returns {Promise} a promise representing notifying CFN of completion; return this to the node runtime