title: Laravel 5.2 Entrust migrate error, cannot add foreign key constraints
body: <p>I installed and configure the Laravel 5.2, its working fine, for <code>User ACL</code> I installed the <code>zizaco/entrust</code> package while running this command <code>php artisan migrate</code> (for creating <code>roles</code>, <code>permissions</code> table etc) getting following error</p>
  
  <blockquote>
    <p>[Illuminate\Database\QueryException]   SQLSTATE[HY000]: General
    error: 1215 Cannot add foreign key constraint (SQL: alter table
    <code>role_user</code> add constraint role_user_user_id_foreign foreign key
    (<code>user_id</code>) references ``    (<code>id</code>) on delete cascade on update
    cascade)</p>
    
    <p>[PDOException]   SQLSTATE[HY000]: General error: 1215 Cannot add
    foreign key constraint</p>
  </blockquote>
  
  <p>What could be the reason ? am I missing something ? I followed the step wise guideline from entrust <a href="https://packagist.org/packages/zizaco/entrust">site</a></p>