Validators.pattern ionic 3

Como fazer funcionar o validator para CPF? O exemplo dele no construtor:

  constructor(public navCtrl: NavController,
    public formBuilder: FormBuilder,
    public alertCtrl: AlertController) {
    this.usuario = this.formBuilder.group({
      cpf: ['', Validators.compose([Validators.pattern('/^[0-9]{3}.?[0-9]{3}.?[0-9]{3}-?[0-9]{2}/'),Validators.required])],
      senha: ['', Validators.compose([Validators.minLength(4),Validators.required])]
    });
  }