WIP: Support for capybara 2.3

I'm going to implement the support for capybara 2.3, keep the pull request open until it's finished :)
@yaauie we are kind of retesting the capybara behaviour here, introduced on `Capybara::Poltergeist::Browser#visit`.

I mean, we are setting the capybara minimum version to 2.3, which has this behaviour.

What do you think? Keep this scenario?