set 'archive_fmt' values

These are going to be used to create an unique id for each image.

gallery_dl/extractor/readcomiconline.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-# Copyright 2016-2017 Mike Fährmann
+# Copyright 2016-2018 Mike Fährmann
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 as
@@ -18,6 +18,7 @@ class ReadcomiconlineExtractor(kissmanga.KissmangaExtractor):
     category = "readcomiconline"
     directory_fmt = ["{category}", "{comic}", "{issue:>03}"]
     filename_fmt = "{comic}_{issue:>03}_{page:>03}.{extension}"
+    archive_fmt = "{comic}_{issue}_{page}"
     root = "http://readcomiconline.to"
 
     def __init__(self, match):