`get` keyword does not allow numeric keys to be used

[rwjblue]

Due to this line, using get with a numeric key does not work properly.

  model() {
    return {
      indexes: [2,3,4],
      items: {
        2: 'blah',
        3: 'zorz',
        4: 'derp'        
      }
    }
  },

    <ul>
      {{#each model.indexes as |index|}}
        <li>{{get model.items index}}</li>
      {{/each}}
    </ul>

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Demo: http://rwjblue.jsbin.com/loneva/edit?html,js,output