Run
vagrant box add discourse/discourse-1.3.0 '..\discourse-1.3.0.box'
instead of
vagrant box add discourse-1.3.0 '..\discourse-1.3.0.box'
Run
vagrant box add discourse/discourse-1.3.0 '..\discourse-1.3.0.box'
instead of
vagrant box add discourse-1.3.0 '..\discourse-1.3.0.box'