docs(README): update links to 0.2.18

Author: christopherthielen

README.md

@@ -2,7 +2,7 @@
 
 #### The de-facto solution to flexible routing with nested views
 ---
-**[Download 0.2.17](http://angular-ui.github.io/ui-router/release/angular-ui-router.js)** (or **[Minified](http://angular-ui.github.io/ui-router/release/angular-ui-router.min.js)**) **|**
+**[Download 0.2.18](https://cdn.rawgit.com/angular-ui/ui-router/0.2.18/release/angular-ui-router.js)** (or **[Minified](https://cdn.rawgit.com/angular-ui/ui-router/0.2.18/release/angular-ui-router.min.js)**) **|**
 **[Guide](https://github.com/angular-ui/ui-router/wiki) |**
 **[API](http://angular-ui.github.io/ui-router/site) |**
 **[Sample](http://angular-ui.github.com/ui-router/sample/) ([Src](https://github.com/angular-ui/ui-router/tree/gh-pages/sample)) |**