example(ts/toh-4,5): getHeroesSlowly() to return getHeroes()

Have `getHeroesSlowly()` delay and then return the value of
`getHeroes()`. This makes it easier for user’s performing the tutorial
to keep this slower method as they evolve toh-5 into toh-6.

Author: chalin

public/docs/_examples/toh-4/ts/app/hero.service.1.ts

@@ -13,8 +13,7 @@ export class HeroService {
   // #enddocregion empty-class, getHeroes-stub, full
   /*
   // #docregion getHeroes-stub
-  getHeroes(): void {
-  }
+  getHeroes(): void {} // stub
   // #enddocregion getHeroes-stub
   */
   // #docregion full

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

@@ -18,8 +18,8 @@ export class HeroService {
   // #docregion get-heroes-slowly
   getHeroesSlowly(): Promise<Hero[]> {
     return new Promise<Hero[]>(resolve =>
-      setTimeout(() => resolve(HEROES), 2000) // 2 seconds
-    );
+      setTimeout(resolve, 2000)) // delay 2 seconds
+      .then(() => this.getHeroes());
   }
   // #enddocregion get-heroes-slowly
   // #docregion

public/docs/_examples/toh-5/ts/app/hero.service.ts

@@ -10,11 +10,10 @@ export class HeroService {
     return Promise.resolve(HEROES);
   }
 
-  // See the "Take it slow" appendix
   getHeroesSlowly(): Promise<Hero[]> {
     return new Promise<Hero[]>(resolve =>
-      setTimeout(() => resolve(HEROES), 2000) // 2 seconds
-    );
+      setTimeout(resolve, 2000)) // delay 2 seconds
+      .then(() => this.getHeroes());
   }
 
   // #docregion getHero