use lambda to meet rails4 requirement that scopes respond to call

lib/attr_enumerator.rb

@@ -9,14 +9,14 @@ def attr_enumerator(attribute, choices, options = {})
       constant = options.delete(:constant) || attribute.to_s.pluralize.upcase
       prefix = options[:prefix] ? options.delete(:prefix).to_s + '_' : ''
       options[:message] ||= :invalid
-      
+
       const_set(constant, choices).freeze
       validates_inclusion_of attribute, options.merge(:in => choices)
 
       choices.each do |choice|
         choice_string = prefix + choice.to_s.underscore.parameterize('_')
         define_method(choice_string + '?') { send(attribute) == choice }
-        scope choice_string, where(attribute => choice) if respond_to? :scope
+        scope choice_string, lambda { where(attribute => choice) } if respond_to? :scope
       end
     end
   end