docs(annotations): correct List for directives for Component

@Component takes a List of directives

https://github.com/angular/angular/blob/master/modules/angular2/src/core
/annotations_impl/annotations.js#L867

modules/angular2/src/core/annotations_impl/annotations.js

@@ -832,7 +832,7 @@ export class Component extends Directive {
    * })
    * @View({
    *   template: `{{greeter.greet('world')}}!`,
-   *   directives: Child
+   *   directives: [Child]
    * })
    * class HelloWorld {
    *   greeter:Greeter;