Bugfix: undefined method root for Capybara::Rails:Module

Bug using capybara-screenshot with minitest-rails-capybara.

Gemfile:
group :test do
# Pretty printed test output
gem 'turn', :require => false
gem 'minitest-rails', '>=0.9.1'
gem 'minitest-rails-capybara', '>=0.9.0'
gem 'poltergeist'
gem 'launchy'
gem 'capybara-screenshot'
end

undefined method root' for Capybara::Rails:Module
ExceptionNoMethodError' at:
capybara-screenshot/lib/capybara-screenshot.rb:47:in capybara_root'
capybara-screenshot/lib/capybara-screenshot/saver.rb:41:inscreenshot_path'
capybara-screenshot/lib/capybara-screenshot/saver.rb:33:in save_screenshot'
capybara-screenshot/lib/capybara-screenshot/saver.rb:17:insave'
capybara-screenshot/lib/capybara-screenshot.rb:25:in screenshot_and_open_image'
capybara-screenshot/lib/capybara-screenshot/capybara.rb:11:inscreenshot_and_open_image'