fix warnings in Ruby 2.0

activesupport/lib/active_support/core_ext/date/calculations.rb

@@ -8,6 +8,8 @@
 class Date
   include DateAndTime::Calculations
 
+  @beginning_of_week_default = nil
+
   class << self
     attr_accessor :beginning_of_week_default
 

activesupport/lib/active_support/core_ext/time/zones.rb

 require 'active_support/time_with_zone'
 
 class Time
+  @zone_default = nil
+
   class << self
     attr_accessor :zone_default