Can not sign up for map-box without a credit card anymore

[Damans227]

For the super-rentals tutorial documentation available here:

Managing Application-level Configurations

A credit card is now required to sign up for the Map-Box API and it seems you can't do it without one. You can pay through Stripe by clicking the map-box link in the Ember-Js documentation. Here is a screen shot:

Therefore, the following line in the documentation is no longer valid:

We will use the [Mapbox](https://www.mapbox.com/) API to generate maps for our rental properties. You can [sign up](https://www.mapbox.com/signup/) for free and without a credit card.