Add missing import of Injectable to DI guide

closes #373

public/docs/ts/latest/guide/dependency-injection.jade

@@ -316,6 +316,7 @@ include ../../../../_includes/_util-fns
 
   Here's a rewrite of `HeroService` with a new constructor that takes a `logger` parameter.
   ```
+  import {Injectable} from 'angular2/angular2';
   import {Hero} from './hero';
   import {HEROES} from './mock-heroes';
   import {Logger} from './logger';