title: ImmutableJS: merge two list of objects, without duplicating them
body: <p>Supposing I have the below:</p>
  
  <pre><code>var allFoods = Immutable.List();
  
  var frenchFood = Immutable.List([
    {
    'type': 'french fries',
    'price': 3
    },
    {
      'type': 'petit gateau',
      'price': 40
    },
    {
      'type': 'croissant',
      'price': 20
    },
  ]);
  
  var fastFood = Immutable.List([
    {
    'type': 'cheeseburger',
    'price': 5
    },
    {
    'type': 'vegan burger',
    'price': 20
    },
    {
    'type': 'french fries',
    'price': 3
    }
  ]);
  </code></pre>
  
  <p>I want to merge both lists, in a way that I also remove dupes (in this case, <em>french fries</em>), so the expected result would be:</p>
  
  <pre><code>{
  'type': 'french fries', // keep the first french fries
  'price': 3
  },
  {
    'type': 'petit gateau',
    'price': 40
  },
  {
    'type': 'croissant',
    'price': 20
  },
    {
  'type': 'cheeseburger',
  'price': 5
  },
  {
  'type': 'vegan burger',
  'price': 20
  }
  </code></pre>
  
  <p>What I'm trying (doesn't remove dupes):</p>
  
  <pre><code>allFoods = frenchFood.concat(fastFood);
  allFoods = allFoods.filter(function(item, pos) {
      return allFoods.indexOf(item) === pos;
  });
  </code></pre>
  
  <p>Which returns arrays merged, but still duplicated.</p>
  
  <p>What am I missing?</p>