include Capybara::DSL rather than Capybara

So today, we noticed that your gem was throwing a deprecation warning for including Capybara, rather than Capybara::DSL. So we fixed it. :banana: 

Thanks for making a cool thing :] 

-Neil
Merge pull request #131 from BananaNeil/patch-1

include Capybara::DSL rather than Capybara