fix(location): dartium does not like pushState with null.

According to
https://developer.mozilla.org/en-US/docs/Web/Guide/API/DOM/Manipulating_the_browser_history
the value of the title parameter is irrelevant anyways.

modules/angular2/src/router/location.js

@@ -36,7 +36,7 @@ export class Location {
 
   go(url:string) {
     url = this._stripBaseHref(url);
-    this._browserLocation.pushState(null, null, url);
+    this._browserLocation.pushState(null, '', url);
   }
 
   forward() {