Update a single savings goals data.

def update(self, goal: Dict=None) -> None:
        """Update a single savings goals data."""
        if goal is None:
            endpoint = "/account/{0}/savings-goals/{1}".format(
                self._account_uid,
                self.uid
            )

            response = get(
                _url(endpoint, self._sandbox),
                headers=self._auth_headers
            )
            response.raise_for_status()
            goal = response.json()

        self.uid = goal.get('savingsGoalUid')
        self.name = goal.get('name')

        target = goal.get('target', {})
        self.target_currency = target.get('currency')
        self.target_minor_units = target.get('minorUnits')

        total_saved = goal.get('totalSaved', {})
        self.total_saved_currency = total_saved.get('currency')
        self.total_saved_minor_units = total_saved.get('minorUnits')