slice now returns indifferent hash if called on one

Signed-off-by: Michael Koziarski <michael@koziarski.com>

[#1096 state:committed]

activesupport/lib/active_support/core_ext/hash/slice.rb

@@ -18,7 +18,7 @@ module Slice
         # Returns a new hash with only the given keys.
         def slice(*keys)
           keys = keys.map! { |key| convert_key(key) } if respond_to?(:convert_key)
-          hash = {}
+          hash = self.class.new
           keys.each { |k| hash[k] = self[k] if has_key?(k) }
           hash
         end