Use #deliver_now if using Rails 4.2+

Rails 4.2.0.beta2 deprecates `ActionMailer::MessageDelivery#deliver` in favour of `#deliver_now` and `#deliver_later`.

This removes the deprecation warning produced by calling the `#deliver_reset_password_instructions!` method on the sorcery model when working on 4.2.0.beta2 and above.