Return the default formats, if they apply to the current path #157

def default_formats(self, path):
        """Return the default formats, if they apply to the current path #157"""
        formats = long_form_multiple_formats(self.default_jupytext_formats)
        for fmt in formats:
            try:
                base_path(path, fmt)
                return self.default_jupytext_formats
            except InconsistentPath:
                continue

        return None