title: Crafting a sequelize WHERE IN using multiple columns
body: <p>In MySQL (And other dbs), <a href="https://stackoverflow.com/questions/44706196/mysql-multiple-columns-in-in-clause">you can do a where in query with multiple columns</a> like below:</p>
  
  <pre><code>SELECT * FROM trains WHERE (name, location) IN (('train1', 'us'), ... ,('train2', 'us'));
  </code></pre>
  
  <p>I'm trying to do this with sequelize:</p>
  
  <pre><code>const selectTrains = [
      {name: 'train1', location: 'us'},
      {name: 'train1', location: 'eu'},
      {name: 'train2', location: 'us'},
  ];
  
  let dbTrains = await Trains.findAll({ where: { [Op.in]: selectTrains} });
  </code></pre>
  
  <p>But I get the following error:</p>
  
  <blockquote>
    <p>UnhandledPromiseRejectionWarning: Error: Invalid value {name: 'train1', location: 'us'}</p>
  </blockquote>
  
  <p>The documentation didn't really cover this use case. Is this possible to do with the <code>Op.in</code> operator?</p>