API integration not working

https://github.com/akveo/ng2-smart-table/blob/master/src/app/pages/examples/server/advanced-example-server.component.ts i am trying fetch data from an API like how its shown in the above link but its not working. it still shows no data found in the smart table . but in console it shows something like "Please check that data extracted from the server response by the key '' exists and is array.
Error: Data must be an array." can any 1 help .this is the api whic i used 'https://address-book-demo.herokuapp.com/api/contacts'