message: docs: update tagline
  Seems like the tagline has changed on the [Angular Twitter account](https://twitter.com/angular) and angular.io. This change makes this doc in line with those two resources.
  PR Close
diff: -<h1 align="center">Angular - One framework. Mobile & desktop.</h1>
  +<h1 align="center">Angular - The modern web developer's platform.</h1>
  <p align="center">
  <img src="aio/src/assets/images/logos/angular/angular.png" alt="angular-logo" width="120px" height="120px"/>
  