allow colours in workers (#335)

browser.js

@@ -42,10 +42,12 @@ function useColors() {
   // document is undefined in react-native: https://github.com/facebook/react-native/pull/1632
   return (typeof document !== 'undefined' && 'WebkitAppearance' in document.documentElement.style) ||
     // is firebug? http://stackoverflow.com/a/398120/376773
-    (window.console && (console.firebug || (console.exception && console.table))) ||
+    (typeof window !== 'undefined' && window.console && (console.firebug || (console.exception && console.table))) ||
     // is firefox >= v31?
     // https://developer.mozilla.org/en-US/docs/Tools/Web_Console#Styling_messages
-    (navigator.userAgent.toLowerCase().match(/firefox\/(\d+)/) && parseInt(RegExp.$1, 10) >= 31);
+    (navigator.userAgent.toLowerCase().match(/firefox\/(\d+)/) && parseInt(RegExp.$1, 10) >= 31) ||
+    // double check webkit in userAgent just in case we are in a worker
+    (navigator.userAgent.toLowerCase().match(/applewebkit\/(\d+)/));
 }
 
 /**