pelican-4.1: (conf) use slug keyword

pelicanconf.py

@@ -19,7 +19,7 @@ FEED_DOMAIN = 'https://gitoyen.net'
 FEED_ALL_ATOM = None
 FEED_ALL_RSS = 'feeds/all.rss.xml'
 CATEGORY_FEED_ATOM = None
-CATEGORY_FEED_RSS = 'feeds/%s.rss.xml'
+CATEGORY_FEED_RSS = 'feeds/{slug}.rss.xml'
 TRANSLATION_FEED_ATOM = None
 AUTHOR_FEED_ATOM = None
 AUTHOR_FEED_RSS = None