fix(PWA): prompt a message when a new ServiceWorker is avaiable (#27)

The implementation was already done but was not triggered

src/app/app.component.ts

@@ -1,11 +1,16 @@
 import { Component, OnInit } from '@angular/core';
 import { environment } from 'src/environments/environment';
+import { PromptUpdateService } from './prompt-update.service';
 
 @Component({
   selector: 'app-root',
   templateUrl: './app.component.html',
   styleUrls: ['./app.component.css']
 })
 export class AppComponent {
-  version = environment.version
+  version = environment.version;
+
+  constructor(private promptUpdateService: PromptUpdateService) {
+    this.promptUpdateService.check();
+  }
 }