ordered_set.rb in madvertise-ext-0.6.6

- old
+ new

@@ -1,5 +1,6 @@
 # http://stackoverflow.com/a/8451605/965088
+require 'set'
 require 'active_support/ordered_hash'
 
 class OrderedSet < Set
   def initialize enum = nil, &block
     @hash = ActiveSupport::OrderedHash.new