Fix template variable for adding h-entry to article

 $if re.match("(19|20)\d\d", tx.request.uri.path):
     $var breadcrumbs = (p.format("MM"), p.format("MMMM"), p.format("DD"), p.format("D"))
 $# var body_classes = ["widescreen"]
-$var classes = ["h-entry"]
+$var article_classes = ["h-entry"]
 
 $# <link rel=alternate type=application/diamond-types href=${permalink}.dt
 $#       title="versioned history of this document"/>