title: How to go back in Ionic 4
body: <p>I want to add a back button in Ionic4(Angular 7).
  But I can't find the proper method in Angular Router.</p>
  
  <p><code>import {Router} from '@angular/router';</code></p>
  
  <p>How do we go back when clicking a button, in the component handler?
  I'd like to implement it using '@angular/router' not '@angular/common' => Location</p>