Cancels a started verification.  Uses PUT to /verifications/<verification_id> interface

        :Args:
          * *verification_id*: (str) Verification ID
        :Kwargs:
          * *reason*: (str) Reason for cancelling the verification

        :Returns: None

def verification_cancel(self, verification_id, reason=None):
        """
        Cancels a started verification.  Uses PUT to /verifications/<verification_id> interface

        :Args:
          * *verification_id*: (str) Verification ID
        :Kwargs:
          * *reason*: (str) Reason for cancelling the verification

        :Returns: None
        """

        data = {
            "cancel": True,
            "cancel_reason": reason
        }

        response = self._put(url.verifications_id.format(id=verification_id), body=data)
        self._check_response(response, 202)