docs(server-communication): grammar fix (#2626)

Author: MarkPieszak

public/docs/ts/latest/guide/server-communication.jade

@@ -403,7 +403,7 @@ code-example(format="." language="javascript").
 block hero-list-comp-add-hero
   :marked
     Back in the `HeroListComponent`, we see that *its* `addHero()` method subscribes to the observable returned by the *service's* `addHero()` method.
-    When the data, arrive it pushes the new hero object into its `heroes` array for presentation to the user.
+    When the data arrives, it pushes the new hero object into its `heroes` array for presentation to the user.
 +makeExample('server-communication/ts/app/toh/hero-list.component.ts', 'addHero', 'app/toh/hero-list.component.ts (addHero)')(format=".")
 
 +ifDocsFor('ts')