Fix SkyTorrents (#3946)

See https://www.reddit.com/r/sickrage/comments/6rji9l/sky_torrents_index_errors/

sickbeard/providers/skytorrents.py

@@ -109,7 +109,7 @@ class SkyTorrents(TorrentProvider):  # pylint: disable=too-many-instance-attribu
                                        'Title={title}'.format(cat=category, title=title), logger.ERROR)
 
                         size = convert_size(info.group('size')) or -1
-                        info_hash = download_url.rsplit('/', 2)[1]
+                        info_hash = item.guid.rsplit('/', 2)[1]
 
                         item = {'title': title, 'link': download_url, 'size': size, 'seeders': seeders, 'leechers': leechers, 'hash': info_hash}
                         if mode != "RSS":