Fix rxjs error in contact test

src/app/core/components/contact/contact.component.spec.ts

@@ -3,7 +3,7 @@ import { async, ComponentFixture, TestBed } from '@angular/core/testing';
 import { ContactComponent } from './contact.component';
 import { ReactiveFormsModule } from '@angular/forms';
 import { EmailService, NotificationService } from '../../services';
-import { BehaviorSubject, Observable } from 'rxjs';
+import { BehaviorSubject, of } from 'rxjs';
 import { Email } from '../../models';
 
 export class NotificationServiceMock {
@@ -11,7 +11,7 @@ export class NotificationServiceMock {
   constructor() { }
 
   send(email: Email) {
-    return Observable.of(null);
+    return of(null);
   }
 
 }