订阅订阅和取消订阅不是一项功能

我试图取消订阅Observable,发现以下错误:

[ts] Property 'unsubscribe' does not exist on type 'Observable<number>'. Did you mean 'subscribe'?

此错误与代码有关: this.subscription.unsubscribe();

以下是整个文件:

import { Component, Input, OnInit } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { IntervalObservable } from 'rxjs/observable/IntervalObservable';

import 'rxjs/add/observable/interval';
import 'rxjs/add/observable/timer';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.sass']
})

export class AppComponent implements OnInit {
  public counting: boolean;
  public triggerBtnText = 'GO!';
  public subscription: Observable<number>;

  @Input() count = 0;

  constructor() {}

  ngOnInit() {
    this.counting = false;
  }

  toggleStopwatch(): any {
    if (this.counting === false) {
      this.counting = true;
      this.triggerBtnText = 'STOP';
      this.updateCount()
    } else {
      this.counting = false;
      this.triggerBtnText = 'GO!';
      this.subscription.unsubscribe();
    }
  }

  updateCount() {
    this.subscription = Observable.interval(1000);
    this.subscription.subscribe(this.counter);
  }

  public counter(value) {
    this.count = value;
    console.log(value);
  }

  resetCount() {
    this.count = 0;
  }

}

https://bitbucket.org/wtkd/learning-rxjs/branch/moving-to-ng