Test against Rails 4.1

@dasch I need your Rails-fu.
```
     NoMethodError:
       undefined method `default_scoped=' for #<Book::ActiveRecord_Relation:0x007fd200e7bf88>
     # ./lib/zombie_record/restorable.rb:180:in `block in with_deleted'
     # ./lib/zombie_record/restorable.rb:180:in `tap'
     # ./lib/zombie_record/restorable.rb:180:in `with_deleted'
     # ./lib/zombie_record/restorable.rb:172:in `deleted'

Finished in 0.3084 seconds
18 examples, 13 failures
```