docs(toh-pt5/dart): fix grammar mistakes (#2057)

Author: benasocj

public/docs/dart/latest/tutorial/toh-pt5.jade

@@ -403,7 +403,7 @@ code-example(format='').
   We import the `OnInit` interface because we'll call the `HeroService` inside the `ngOnInit` component lifecycle hook.
 +makeExample('toh-5/dart/lib/hero_detail_component.dart', 'import-oninit')(format=".")
 :marked
-  We inject the both the `RouteParams` service and the `HeroService` into the constructor as we've done before,
+  We inject both the `RouteParams` service and the `HeroService` into the constructor as we've done before,
   making private variables for both:
 +makeExample('toh-5/dart/lib/hero_detail_component.dart', 'ctor', 'lib/hero_detail_component.dart (constructor)')(format=".")
 :marked
@@ -584,7 +584,7 @@ figure.image-display
 :marked
 .l-sub-section
   :marked
-    The `styleUrls` property is an list of style file names (with paths).
+    The `styleUrls` property is a list of style file names (with paths).
     We could list multiple style files from different locations if we needed them.
     As with `templateUrl`, we must specify the path _all the way back to the application root_.
 :marked