Dump the validators as json inside the _options dictionary with the key `validators`.

def __dump_validators(self):
        """Dump the validators as json inside the _options dictionary with the key `validators`."""
        if hasattr(self, '_validators'):
            validators_json = []
            for validator in self._validators:
                if isinstance(validator, PropertyValidator):
                    validators_json.append(validator.as_json())
                else:
                    raise APIError("validator is not a PropertyValidator: '{}'".format(validator))
            if self._options.get('validators', list()) == validators_json:
                # no change
                pass
            else:
                new_options = self._options.copy()  # make a copy
                new_options.update({'validators': validators_json})
                validate(new_options, options_json_schema)
                self._options = new_options