xvfb-run and minitest-reporters

New features

• We use minitest-reporters, which outputs one line per test, after the test runs. The previous reporter just output a line of dots ... after all tests are completed. So this change makes it easier to watch tests as they complete.
• Our Docker image now includes xvfb-run. This lets you disable Chrome's "headless" option, which can cause -- if you'll excuse the pun -- headaches. Comments in skeleton/run describe how to turn off headless mode, if you want.

Upgrading

If you're upgrading, you'll need to change your spec/spec_helpers.rb. Replace this line:

require 'minitest/ci'

with this:

require 'minitest/reporters'

And replace this part:

Minitest::Ci.report_dir = '/app/reports'

With this:

Minitest::Reporters.use! [
  Minitest::Reporters::SpecReporter.new,
  Minitest::Reporters::JUnitReporter.new('/app/reports')
]