fix default image partial

layouts/partials/commons/image-default.html

 {{ $section_type := .}}
 {{ $use_default := (index site.Params $section_type).default_image}}
-{{ $image := site.Data.website.default_image }}
+{{ $image := site.Data.website.default.image }}
 
 {{ if and $use_default $image }}
   {{ with index site.Params.image_sizes.sections $section_type }}