Travis CI failing on OSX

[paulkernfeld]

I added a stdio option (#22) that shows that the failures are as below. I actually got the same error on my laptop, and I was able to fix it manually by following the instructions from the first comment in this issue for the Ruby version of headless.

> headless@1.1.0 test /Users/travis/build/paulkernfeld/node-headless
> node test/test.js
_XSERVTransmkdir: ERROR: euid != 0,directory /tmp/.X11-unix will not be created.
_XSERVTransSocketUNIXCreateListener: mkdir(/tmp/.X11-unix) failed, errno = 2
_XSERVTransMakeAllCOTSServerListeners: failed to create listener for local
(EE) 
Fatal server error:
(EE) Cannot establish any listening sockets - Make sure an X server isn't already running(EE) 
/Users/travis/build/paulkernfeld/node-headless/test/test.js:5
  throw new Error('Timeout 2 seconds. You don\'t have xvfb installed or someth
        ^
Error: Timeout 2 seconds. You don't have xvfb installed or something else is seriously wrong.
    at options.display.width [as _onTimeout] (/Users/travis/build/paulkernfeld/node-headless/test/test.js:5:9)
    at Timer.listOnTimeout [as ontimeout] (timers.js:121:15)
npm ERR! Test failed.  See above for more details.