Switching to Poltergeist and PhantomJS on Travis-CI. No need to start xvfb
Changed Capybara.javascript_driver from webkit to poltergeist.
* Modified spec/support/capybara.rb to load Poltergeist as the javascript_driver
* Added require 'capybara/poltergeist' to spec/spec_helper.rb
* Added Poltergeist gem to development and test group in Gemfile. Updated Gemfile.lock