name = ExecJS.runtime.name
expected = "Node.js (V8)"

if name != expected
  raise "Your ExecJS runtime is '#{name}' instead of '#{expected}'. Check README."
end

Make sure people use nodejs for ExecJS
Make sure people use nodejs for ExecJS

On OS X screen.css does not render using JavascriptCore as the backend.
In general it's the best strategy to have developers using the same
setup as in production.
