Bad value copyright for attribute name on element meta: Keyword copyright is not registered

Author: dymio

app/views/layouts/application.html.slim

@@ -10,7 +10,6 @@ html lang=I18n.locale
     - if seo.keywords
       meta name="keywords" content=seo.keywords
     // meta name="author" content="Ivan Dymkov"
-    meta name="copyright" content="(c) #{Date.today.year}"
     // meta http-equiv="Reply-to" content="[email protected]"
 
     link rel="author" type="text/plain" href="#{root_path}humans.txt"