docs(tutorial/step0): fix minor typo

Closes angular#4154

Author: rixrix

docs/content/tutorial/step_00.ngdoc

@@ -148,7 +148,7 @@ for most cases. In advanced cases, such as when using script loaders, you can us
 There are 3 important things that happen during the app bootstrap:
 
 1. The {@link api/AUTO.$injector injector} that will be used for dependency injection
-   within this app is created.
+   when this app is created.
 
 2. The injector will then create the {@link api/ng.$rootScope root scope} that will
    become the context for the model of our application.