title: updateExistingPivot() not working
body: <p>I'm trying to update a pivot table like this:</p>
  
  <pre><code>public function updatePermission($id, $permissionId)
  {
      $permissionValue = Input::get('value');
      $user = User::find($id);
  
      $perms = ['value' =&gt; $permissionValue];
      $user-&gt;permissions()-&gt;updateExistingPivot($permissionId, $perms);
  }
  </code></pre>
  
  <p>This pivot has been previously created with:</p>
  
  <pre><code>public function attachPermission($id)
  {
      $permissionId = Input::get('id');
      $permissionValue = Input::get('value');
      $user = User::find($id);
  
      if (!$user-&gt;permissions-&gt;contains($permissionId)) {
  
          $user-&gt;attachPermissionById($permissionId);
          $perms = ['value' =&gt; $permissionValue];
          $user-&gt;permissions()-&gt;updateExistingPivot($permissionId, $perms);
  
      } else {
  
          return Response::json(array('error' =&gt; 'Permission ' . $permissionId . ' is alreay set for user ' . $user-&gt;id));
  
      }
  
      return Response::json(array('role' =&gt; User::with(['roles.permissions', 'permissions', 'students'])-&gt;find($user-&gt;id)));
  }
  </code></pre>
  
  <p>When the updatePermission() method is hit, it passes fine, but it doesn't update the pivot table with the new value. What am I doing wrong here?</p>