title: Module not found error with vis-timeline and angular 8
body: <p>I'm trying to use the "new" forked vis-timeline 5.1.0 with the latest angular 8 version, but I get and error when trying to run the application:</p>
  
  <blockquote>
    <p>[ng] ERROR in
    ./src/app/pages/interventions/interventions-details/interventions-details.page.ts
    [ng] <strong>Module not found: Error: Can't resolve 'vis'</strong> in
    'D:_GIT\appbo\src\app\pages\interventions\interventions-details'</p>
  </blockquote>
  
  <p>I installed vis-timeline via npm:</p>
  
  <pre><code>npm install vis-timeline --save
  </code></pre>
  
  <p>and then, I installed the types:</p>
  
  <pre><code>npm install @types/vis --save-dev
  </code></pre>
  
  <p>On my page I imported the class and tryed to run the app:</p>
  
  <pre><code>import { Timeline, TimelineOptions, DataItem, DataSet } from 'vis';
  
  @Component(
  {
      selector: 'app-interventions-details',
      templateUrl: './interventions-details.page.html',
      styleUrls: ['./interventions-details.page.scss'],
  })
  export class InterventionsDetailsPage extends AppBasePage implements OnInit
  {
      @ViewChild('revisionsTimeline', { static: true }) RevisionsTimeline: ElementRef;
  
      constructor() 
      { 
  
      }
  
      ngOnInit() 
      {
          this.RenderTimeline();
      }
  
      public RenderTimeline()
      {    
          //RANDOM DATA SOURCE FOR TESTING
          var items = new DataSet(
          [
              { id: 1, content: 'item 1', start: '2014-04-20'},
              { id: 2, content: 'item 2', start: '2014-04-14'},
              { id: 3, content: 'item 3', start: '2014-04-18'},
              { id: 4, content: 'item 4', start: '2014-04-16', end: '2014-04-19'},
              { id: 5, content: 'item 5', start: '2014-04-25'},
              { id: 6, content: 'item 6', start: '2014-04-27', type: 'point'}
          ]);
  
          //SOME BASIC PROPS TO CONFIG THE TIMELINE
          let timelineOptions:TimelineOptions = 
          {
              start: '2014-03-10',
              end: '2014-05-10',
              verticalScroll: false,
              editable: false,
              zoomable:true, 
              locale: "pt"
          };
  
          //INIT TIMELINE INSTANCE
          let timeline:Timeline = new Timeline(this.RevisionsTimeline.nativeElement, items, timelineOptions);
      }
  
  }
  </code></pre>
  
  <p>Am I doing something wrong?
  Can someone help me fix the problem?</p>