Fix style issues

markdown.dtx

@@ -26693,7 +26693,7 @@ parsers.ascii_punctuation      = S("!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~")
         assert(type(node) == "string")
         subparsers[path] = subparsers[path] + S(node)
       end
-    end, function(node, path)
+    end, function(_, path)
       if #path > 0 then
         local byte = path:sub(#path, #path)
         local parent_path = path:sub(1, #path-1)