message: docs: fix typo in TOH http section
  PR Close
diff: @@ -347,7 +347,7 @@ Add the following `addHero()` method to the `HeroService` class.
  `HeroService.addHero()` differs from `updateHero` in two ways.
  * it calls `HttpClient.post()` instead of `put()`.
  -* it expects the server to generates an id for the new hero,
  +* it expects the server to generate an id for the new hero,
  which it returns in the `Observable<Hero>` to the caller.
  Refresh the browser and add some heroes.
  