docs(tutorial): fix typo (slowy -> slowly)

closes #1332

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

@@ -377,7 +377,7 @@ code-example(format="." language="html").
   We can simulate a slow connection.
   
   Import the `Hero` symbol and add the following `getHeroesSlowly` method to the `HeroService`
-+makeExample('toh-4/ts/app/hero.service.ts', 'get-heroes-slowly', 'hero.service.ts (getHeroesSlowy)')(format=".")
++makeExample('toh-4/ts/app/hero.service.ts', 'get-heroes-slowly', 'hero.service.ts (getHeroesSlowly)')(format=".")
 :marked
   Like `getHeroes`, it also returns a promise. 
   But this promise waits 2 seconds before resolving the promise with mock heroes.