title: Order by in nested eager loading in sequelize not working
body: <p>i have four model Tehsil, Ilr, Patwar, and Villages.
  and their association is</p>
  
  <p>Tehsil -> 1:m -> Ilr -> 1:m -> Patwar -> 1:m -> Villages</p>
  
  <p>i want to to apply order by on all four of my models.</p>
  
  <p>Query:</p>
  
  <pre><code>var tehsilQuery = {
      include: [{
          model: Ilr,
          as: 'GirdawariKanoongo',
          include: [{
              model: Patwar,
              as: 'GirdawariPatwar',
              include: [{
                  model: Villages,
                  as: 'GirdawariVillages',
              }]
          }]
      }],
      order: [
          ['tehsil_name', 'ASC'],
          [ {model: Ilr, as: 'GirdawariKanoongo'}, 'kanoongo_name', 'ASC'],
          [ {model: Patwar, as: 'GirdawariPatwar'}, 'patwar_area', 'ASC'],
          [ {model: Villages, as: 'GirdawariVillages'}, 'village_name', 'ASC'],
      ]
  };
  return Tehsils.findAll(tehsilQuery);
  
  [Error: 'girdawari_patwar' in order / group clause is not valid association]
  </code></pre>
  
  <p>order by is working if i remove <code>Patwar</code> and <code>Villages</code>(lat two model) from <code>order</code>.</p>