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/pixnet.py

@@ -169,7 +169,7 @@ class PixnetUserExtractor(PixnetExtractor):
     """Extractor for all sets and folders of a pixnet user"""
     subcategory = "user"
     url_fmt = "{}{}/album/list"
-    pattern = BASE_PATTERN + r"()(?:/blog|/album(?:/list)?)?/?(?:$|[?&#])"
+    pattern = BASE_PATTERN + r"()(?:/blog|/album(?:/list)?)?/?(?:$|[?#])"
     test = (
         ("https://albertayu773.pixnet.net/"),
         ("https://albertayu773.pixnet.net/blog"),