Cleaned up string detection for a deprecation warning by using six.string_types.

    function. This may only be used in the root URLconf, not in an included

    URLconf.

    """

    if isinstance(prefix, (six.text_type, str)):

    if isinstance(prefix, six.string_types):

        warnings.warn(

            "Calling i18n_patterns() with the `prefix` argument and with tuples "

            "instead of django.conf.urls.url() instances is deprecated and "