remove '&' from URL patterns

'/?&#' -> '/?#' and '?&#' -> '?#'

According to https://www.ietf.org/rfc/rfc3986.txt, URLs are
"organized hierarchically" by using "the slash ("/"), question
mark ("?"), and number sign ("#") characters to delimit components"

gallery_dl/extractor/slickpic.py

@@ -33,7 +33,7 @@ class SlickpicAlbumExtractor(SlickpicExtractor):
                      "{album[id]} {album[title]}")
     filename_fmt = "{num:>03}_{id}{title:?_//}.{extension}"
     archive_fmt = "{id}"
-    pattern = BASE_PATTERN + r"/albums/([^/?&#]+)"
+    pattern = BASE_PATTERN + r"/albums/([^/?#]+)"
     test = (
         ("https://mattcrandall.slickpic.com/albums/LamborghiniMurcielago/", {
             "url": "58bd94ebc80fd906e9879826970b408d54c6da07",