title: Alter table field's attribute value to UNSIGNED - Mysql laravel migration
body: <p>Trying to alter table 'role_user' to change the field 'user_id' attribute to 'unsigned' to add a foreign key constraint</p>
  
  <pre><code> Schema::table('role_user', function (Blueprint $table) {
              $table-&gt;integer('user_id')-&gt;unsigned()-&gt;nullable()-&gt;change(); 
              $table-&gt;foreign('user_id')-&gt;references('id')-&gt;on('users')-&gt;onDelete('cascade');
          });
  </code></pre>
  
  <p>Is it right way to change field's attribute value?</p>
  
  <p>I am getting runtime exception <code>'Changing columns for table "role_users" requires Doctrine DBAL';</code></p>