Fix avoid hang in web worker unit test for phantomjs.

Former-commit-id: 22b4e7c99f9b0eb3cf7c250144bb375aeb9352e8

test/test.js

@@ -12,7 +12,7 @@
       slice = Array.prototype.slice,
       system = window.system,
       toString = Object.prototype.toString,
-      Worker = window.Worker;
+      Worker = !phantom && window.Worker;
 
   /** Use a single "load" function */
   var load = !amd && typeof require == 'function' ? require : window.load;