Change capybara dep

This PR changes capybara version requirement. Capybara 2.2 does not introduce breaking changes between 2.1 (https://github.com/strzalek/capybara/blob/master/History.md#version-220) so it allows versions higher or equal than 2.1.

I've bumped up gem version, if this PR is going to be accepted it would be nice to push new gem release as well.

Thanks.