docs(Tutorial): minor repairs to toh-4

close #602
John's comments
Fix for https://github.com/johnpapa/angular2-tour-of-heroes/issues/41

public/docs/_examples/toh-4/ts/app/hero.service.ts

@@ -15,7 +15,7 @@ export class HeroService {
   // See the "Take it slow" appendix
   //#docregion get-heroes-slowly
   getHeroesSlowly() {
-    return new Promise(resolve =>
+    return new Promise<Hero[]>(resolve =>
       setTimeout(()=>resolve(HEROES), 2000) // 2 seconds
     );
   }

public/docs/ts/latest/tutorial/toh-pt4.jade

@@ -156,7 +156,7 @@ code-example(format="." language="bash").
   Will we need different mocked versions under test?
   Not easy.
   
-  *What if ... what if ... Dude! We've got work to do!*
+  *What if ... what if ... Hey, we've got work to do!*
   
   We get it. Really we do. 
   But it is so ridiculously easy to avoid these problems that there is no excuse for doing it wrong.
@@ -303,6 +303,10 @@ code-example(format="." language="html").
   
   We pass our callback function as an argument to the promise's **then** method:
 +makeExample('toh-4/ts/app/app.component.ts', 'get-heroes', 'app.component.ts (getHeroes - revised)')(format=".")
+.l-sub-section
+  :marked
+    The [ES2015 arrow function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions)
+    in the callback is more succint than the equivalent function expression and gracefully handles *this*.
 :marked
   Our callback sets the component's `heroes` property to the array of heroes returned by the service. That's all there is to it!
   
@@ -382,10 +386,8 @@ code-example(format="." language="html").
   ### Appendix: Shadowing the parent's service
   
   We stated [earlier](#child-component) that if we injected the parent `AppComponent` `HeroService`
-  into the `HeroDetailComponent`, *we must not add a providers array* like the following
-  to the  `HeroDetailComponent`.
-+makeExample('toh-4/ts/app/app.component.1.ts', 'providers', 'No! Don\'t do this!')
-:marked
+  into the `HeroDetailComponent`, *we must not add a providers array* to the `HeroDetailComponent` metadata.
+
   Why?  Because that tells Angular to create a new instance of the `HeroService` at the `HeroDetailComponent` level.
   The `HeroDetailComponent` doesn't want its *own*  service instance; it wants its *parent's* service instance.
   Adding the `providers` array creates a new service instance that shadows the parent instance.