updated deprecated cgi.parse_qsl to use six's parse_qsl

[VKen]

According to Python 2 documentation: https://docs.python.org/2/library/cgi.html#cgi.parse_qsl

"This function is deprecated in this module. Use urlparse.parse_qsl() instead. It is maintained here only for backward compatiblity."

For future compatibility with Python 3, the scrapy.utils.url module is updated to use six library's urllib.parse.parse_qsl instead.
https://pythonhosted.org/six/#module-six.moves.urllib.parse

[kmike]

Thanks!