Capistrano v3 fixes for bugsnag v2+

@ConradIrwin ping. a couple of clarifications:

* `require "bugsnag/deploy"` for `Bugsnag::Deploy.notify` method to be available in Capistrano v2 & v3.
*  `run_locally` so the logger method `info` & `error` will be available (`important` doesn't exists in cap v3)