docs(toh-pt6,guide): fix a grammatical error (#2594)

Author: timofeysie

public/docs/ts/latest/guide/router.jade

@@ -1182,7 +1182,7 @@ h3#merge-hero-routes Import hero module into AppModule
   We imported the `HeroesModule` and added it to our `AppModule`'s `imports`.
 
   We removed the `HeroListComponent` from the `AppModule`'s `declarations` because its being provided by the `HeroesModule`
-  now. This is important because their can be only **one** owner for a declared component. In our case, the `Heroes` module is
+  now. This is important because there can be only **one** owner for a declared component. In our case, the `Heroes` module is
   the owner of the `Heroes` components and is making them available to the `AppModule`.
 
 .l-sub-section