Fixed broken Chargify.site

![](http://media3.giphy.com/media/sLyeURTOizFXa/200.gif)

We were running the version `0.5.0` and we recently updated to the latest and we found out that recently `Chargify.site` was broken. The bug was introduced on https://github.com/chargify/chargify_api_ares/pull/62 while refactoring the configuration. We rely on that attribute to generate links to update payments.