title: Unique constraint on sequelize column
body: <p>Using NodeJS and Sequelize 2.0, I'm writing a migration to create a new table. In addition to the primary key, I want to mark a second column to be enforced as unique. I can't find anything about this in the documentation.</p>
  
  <pre><code>migration.createTable('data', {
      id: {
          type: DataTypes.INTEGER,
          primaryKey: true,
          autoIncrement: true
      },
      key: {
          // needs to be unique
          type: DataTypes.UUID,
          allowNull: false
      }
  })
      .then(function () {
          done();
      });
  </code></pre>