title: Sequelize: update by column it's old value
body: <p>i am trying to update a set of data using Sequelize by this query </p>
  
  <pre><code>Users.update({
      flag: 'flag &amp; ~ 2'
  } , {
      where : {
          id :{
              gt : 2
          }
      }
  })
  </code></pre>
  
  <p>the generated query is</p>
  
  <pre><code>UPDATE `users` SET `flag`='flag &amp; ~ 2' WHERE id &gt; 2
  </code></pre>
  
  <p>But is should be </p>
  
  <pre><code>UPDATE `users` SET `flag`=flag &amp; ~ 2 WHERE id &gt; 2
  </code></pre>
  
  <p>so my question is how can i update data by by it's old value </p>
  
  <p>Regards</p>