Fixed typo in internal CharField method

    def check(self, **kwargs):

        errors = super(CharField, self).check(**kwargs)

        errors.extend(self._check_max_length_attibute(**kwargs))

        errors.extend(self._check_max_length_attribute(**kwargs))

        return errors

    def _check_max_length_attibute(self, **kwargs):

    def _check_max_length_attribute(self, **kwargs):

        try:

            max_length = int(self.max_length)

            if max_length <= 0: