ember-lifeline - cancelPoll not working

controllers.application.js

import Ember from 'ember';
import { runTask, pollTask, cancelPoll } from 'ember-lifeline';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  count: 0,
  
  actions: {
    startPoll() {
      this.set('isPolling', true);
      
      this.pollToken = pollTask(this, (next) => {
        this.incrementProperty('count');
        runTask(this, next, 1000);
      });
    },
    
    stopPoll() {
    	this.set('isPolling', false);
      cancelPoll(this, this.pollToken);
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>

{{outlet}}

{{#if isPolling}}
  <button {{action "stopPoll"}}>Stop poll</button>
{{else}}
  <button {{action "startPoll"}}>Start poll</button>
{{/if}}

<br>
<br>
Counter: {{count}}

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2",
    "ember-lifeline": "3.0.9"
  }
}