Update demo link in Readme

Demo link in readme points to forked plnkr that makes use of ui-select v0.2.0 (from src) and demonstrates markup with updated directives
choices -> ui-select-choices
match -> ui-select-match

Author: duncanbeevers

README.md

@@ -2,7 +2,7 @@
 
 AngularJS-native version of [Select2](http://ivaynberg.github.io/select2/) and [Selectize](http://brianreavis.github.io/selectize.js/).
 
-- [Demo](http://plnkr.co/edit/GtOOWE?p=preview)
+- [Demo](http://plnkr.co/edit/bgXrCxZYlt99fquw7mce?p=preview)
 - [Bootstrap theme](http://plnkr.co/edit/7Fpbtg?p=preview)
 
 ## Features