Adding http headers in Angular 6

The correct way to set headers is

let headers: HttpHeaders = new HttpHeaders();
headers = headers.append('Accept', 'application/json');
headers = headers.append('zumo-api-version', '2.0.0');

Angular 6 format:

let headers = new HttpHeaders({
    'Accept': 'application/json',
    'zumo-api-version': '2.0.0'
});