making sure that active_merchant will work without loading rails

This fixes issue:
```activemerchant-1.42.4/lib/active_merchant/billing/gateways/authorize_net.rb:298:in `success?': undefined method `exclude?' for ["310", "311"]:Array (NoMethodError)
(...)
from payment.rb:20:in `<main>'```

when used without using rails / manually requiring 'active_support/core_ext/enumerable.rb'  first.