Treat absent files as empty when changes script

Hi,

The `check_for_changes_script` method don't treat diff to new files. I try use this rake to skip rails seed:

```ruby
desc "Seeding data to Database."
task :'db_seed' do
  seed_files = Dir['db/seeds/*.rb']
  seed_files.push("db/seeds.rb")

  queue check_for_changes_script({
    check: 'db/seeds.rb',
    at: seed_files,
    skip: %[
      echo "-----> DB seed unchanged; skipping DB seed"
    ],
    changed: %[
      echo "-----> Seeding database"
      #{echo_cmd %[#{rake} db:seed]}
    ],
    default: %[
      echo "-----> Seeding database"
      #{echo_cmd %[#{rake} db:seed]}
    ]
  })
end
```
Then, using -N param in diff command for treat absent files as empty. :smile: