Link to sample app source in master branch

The Sample App source linked to the branch 'ui-states' which has been merged to master. 

The application running on http://angular-ui.github.io/ui-router/sample/ has animations enabled, so I assume it is based on the master branch. It's probably better to link to the actual source of the sample.

Author: tfnico

README.md

@@ -41,7 +41,7 @@ To evolve the concept of an Angular "Route" into a more general concept of a "St
 
 * [In-Depth Overview](https://github.com/angular-ui/ui-router/wiki)
 * [FAQ](https://github.com/angular-ui/ui-router/wiki/Frequently-Asked-Questions)
-* [Sample App](http://angular-ui.github.com/ui-router/sample/) ([Source](https://github.com/angular-ui/ui-router/tree/ui-states/sample))
+* [Sample App](http://angular-ui.github.com/ui-router/sample/) ([Source](https://github.com/angular-ui/ui-router/tree/master/sample))
 * [Generated Docs](http://angular-ui.github.com/ui-router/build/doc/)
 * Latest build: [angular-ui-states.min.js](http://angular-ui.github.com/ui-router/build/angular-ui-states.min.js)
   (uncompressed [angular-ui-states.js](http://angular-ui.github.com/ui-router/build/angular-ui-states.js))