title: sequelize.js - adding a column as a composite primary key
body: <p>I have a table - <code>source_rule_role</code> with two composite primary key: ruleId, roleId.</p>
  
  <p>I need to add another column - rowNum, that the new primary key will be composite of three columns: ruleId, roleId, rowNum.</p>
  
  <p>I tried in my migration:</p>
  
  <pre><code>...
  .then(() =&gt; { 
  migration.addColumn(
      'source_rule_role',
      'rowNum',
      {
          type: DataTypes.INTEGER,
          allowNull: false,
          primaryKey: true,
          defaultValue: 1
      })
  })
  ...
  </code></pre>
  
  <p>but I get a Multiple primary key defined error.</p>
  
  <p>When I add the rowNum column, not as a primary key, it works.</p>