message: docs(router): fix minor grammatical issue
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diff: This tutorial describes how you can build a single-page application, SPA that uses multiple Angular routes.
  -In an SPA, all of your application's functions exist in a single HTML page.
  +In a Single Page Application (SPA), all of your application's functions exist in a single HTML page.
  As users access your application's features, the browser needs to render only the parts that matter to the user, instead of loading a new page. This pattern can significantly improve your application's user experience.
  To define how users navigate through your application, you use routes. You can add routes to define how users navigate from one part of your application to another.
  