Travis: run 'rake spec' under xvfb
Travis: run 'rake spec' under xvfb

so Capybara can find & drive Firefox for feature specs
w/ "js: true"

cf http://docs.travis-ci.com/user/gui-and-headless-browsers/#Using-xvfb-to-Run-Tests-That-Require-GUI-(e.g.-a-Web-browser)

ddmck/Empirical-Core,ddmck/Empirical-Core,ddmck/Empirical-Core,ddmck/Empirical-Core