Add an empty afterAll to the TestBed exmaple (NativeScript#1871)

This fixes JS: NSUTR: this.error: An error was thrown in afterAll JS: TypeError: Cannot read property 'origin' of undefined NativeScript / 29 (10; Android SDK built for x86) undefined at line undefined FAILED An error was thrown in afterAll TypeError: Cannot read property 'origin' of undefined at <Jasmine> at ZoneQueueRunner.push.../node_modules/@nativescript/angular/zone-js/dist/zone-nativescript.jasmine.js.jasmine.QueueRunner.ZoneQueueRunner.execute (file:///data/data/org.nativescript.firstapp/files/app/vendor.js:84532:42) at <Jasmine> NativeScript / 29 (10; Android SDK built for x86): Executed 1 of 1 (1 FAILED) (0.237 secs / 0 secs)

Author: scieslak

docs/tooling/testing/testing.md

@@ -177,6 +177,7 @@ export class ZonedRenderer {
 describe('Renderer E2E', () => {
  beforeEach(nsTestBedBeforeEach([ZonedRenderer]));
  afterEach(nsTestBedAfterEach(false));
+ afterAll(() => {});
 
  it('executes events inside NgZone when listen is called outside NgZone', async(() => {
  const eventName = 'someEvent';