fix design upload

app/views/admin/designs/_form.html.erb

@@ -36,7 +36,7 @@
         <a class="remove_mark" href="#">Del</a></li>
     <% end %>
     </ul>
-  <%= fields_for "design[stylesheet][]", @design, :index => nil do |f| %>
+  <%= fields_for "design[stylesheets][]", @design, :index => nil do |f| %>
     <%= f.file_field :file ,{:class=>"multi_files",:rtype=>"stylesheets"}%>
   <% end %>
 </p>