basePath should be considered part of the trails path

[elbrujohalcon]

Even when #22 is fixed by just setting basePath => "", sometimes having a basePath (e.g. /admin/api) is actually useful, but swagger has to consider that such a basePath will be included in the trails routes, at least until inaka/cowboy-trails#22 is implemented. And in that case, basePath should be taken from there and not as an extra swagger property.

[Euen]

Var baseUrl needs to be updated to change this text field adding the corresponding api_root

e.g. change

http://localhost:8383/api-docs/swagger.json

to

http://localhost:8383/admin/api/api-docs/swagger.json