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/8kun.py

@@ -64,7 +64,7 @@ class _8kunBoardExtractor(Extractor):
     """Extractor for 8kun boards"""
     category = "8kun"
     subcategory = "board"
-    pattern = r"(?:https?://)?8kun\.top/([^/?&#]+)/(?:index|\d+)\.html"
+    pattern = r"(?:https?://)?8kun\.top/([^/?#]+)/(?:index|\d+)\.html"
     test = (
         ("https://8kun.top/v/index.html", {
             "pattern": _8kunThreadExtractor.pattern,