fix for Procfile create/update: newline added to the end of content

This fix was made for a tiny bug fix.
For example, we have following defaults:

    recipes:
    - gems
    - email_dev
    prefs:
      :dev_webserver: thin
      :prod_webserver: puma
      :mailcatcher: true

In this case we'll have following `Procfile.dev`:

    web: bundle exec rails server -p $PORTmail: mailcatcher --foreground

So we just need to add `\n` to the end of each `Procfile` line.