How to update nested object in Ember

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  critService: Ember.inject.service(),
  init(){
    this._super(...arguments);
    this.get('critService').loadCrits();
  }, 
    actions: {
        modifyCrit(crit) {                      
            crit.set('value',1000);                      
        }
    }
});

services.crit-service.js

import Ember from 'ember';

const KeyVal = Ember.Object.extend({
  key: null,
  value: null
});

export default Ember.Service.extend({
    crits: null,
    loadCrits() {
        var newCrits = Ember.A();
        var max = Math.random() * 10;
        for(var i=0; i<max; i++) {
            var crit = Ember.A();
            var num = Math.random() * 5;
            for(var j=0; j<num; j++) {
              let item = KeyVal.create({key: "data"+j, value: j});
              crit.pushObject(item);                
            }
          let newItem = KeyVal.create({key: "crit"+i, value: crit});
          newCrits.pushObject(newItem);
        }

        this.set("crits", newCrits);
    }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<table>
    {{#each critService.crits as |crit|}}
    <tr>
        <td>{{crit.key}}</td>
        <td><ul>
            {{#each crit.value as |k|}}
                <li>
                    {{k.key}} = {{k.value}}
                    <button {{action "modifyCrit"  k}}>change</button>
                </li>
            {{/each}}
        </ul></td>
    </tr>
    {{/each}}
</table>
<br>
<br>

twiddle.json

{
  "version": "0.10.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.6.0",
    "ember-data": "2.6.1",
    "ember-template-compiler": "2.6.0"
  },
  "addons": {}
}