title: Laravel Migration: auto increment key when it is not primary
body: <p>I'm trying to create a table with Laravel migrations but I'm having some trouble.
  I just need to create a table with a primary pair ('id' and 'revision'), being 'id' an auto increment.
  I can do it in MySQL, but I can't manage to do it with Laravel Migrations since increments() also set the field as primary.
  So far I have this:</p>
  
  <pre><code>Schema::create('bibliographies', function(Blueprint $table)
      {
          $table-&gt;increments('id');
          $table-&gt;integer('revision');
          ...
          $table-&gt;timestamps();
          $table-&gt;softDeletes();
          $table-&gt;primary(array('id', 'revision'));
      });
  </code></pre>
  
  <p>Note: changing increments() method is not an option since it is Laravel core.</p>
  
  <p>Thank you for your help in advance.</p>