Make Rails a soft dependence

[do-you-dare]

While I believe most of the uses of gisdatigo will be updating rails projects, there´s nothing intrinsically dependent on rails here besides the railties defining the rake task.

Rails could still be present as a development dependence maybe, so that the integration can be tested. This way an end user that wants to use gisdatigo to update his non rails project can install it without pulling rails.

Does this make sense?

[rafamanzo]

I think this is related to the gisdatigo:run task. It may be possible to depend only on one of Rails' gems.