Update image card to support html in description

Changes image card description from using a p tag to a div tag, so it can support html

lib/govuk_publishing_components/presenters/image_card_helper.rb

@@ -49,7 +49,7 @@ def heading_tag
       end
 
       def description
-        content_tag(:p, @description, class: "gem-c-image-card__description") if @description
+        content_tag(:div, @description, class: "gem-c-image-card__description") if @description
       end
     end
   end