Try upgrading Phantom

Looks like we were on an old version initially because of
mocha-phantomjs, but we're using Karma now and that appears to work with
newer ones.

I'm also hoping using 2.x.x will mean that the version Travis has
installed will allow us to sidestep 403 errors from PhantomJS's hosting:
https://travis-ci.org/mochajs/mocha/jobs/131535241

package.json

@@ -294,7 +294,7 @@
     "karma-phantomjs-launcher": "^0.2.3",
     "karma-sauce-launcher": "^1.0.0",
     "karma-should": "^1.0.0",
-    "phantomjs": "1.9.8",
+    "phantomjs": "2.0.0",
     "should": "~8.0.0",
     "through2": "~0.6.5",
     "watchify": "^3.7.0"