add tty? method to Job model which acts as Capistrano::Logger

* actual for Capistrano since version 2.13.5

Собственно - вот https://github.com/capistrano/capistrano/blob/master/lib/capistrano/logger.rb#L86 
и вот https://github.com/express42/strano/blob/master/app/models/job.rb#L24