Fix reference for HTML5 Vaidations

Author: ElliottAYoung

app/cells/plugins/core/cell.rb

@@ -4,7 +4,7 @@ class Cell < FieldCell
       view_paths << "#{Cortex::Plugins::Core::Engine.root}/app/cells"
 
       def required?
-        field_item.field.validations["presence"]
+        field.validations["presence"]
       end
     end
   end