class 'form' not found in laravel 5.2

I have followed these steps as answered in similar questions here but, i don't get a solution:

1. edited composer.json to add:

   "require": { "laravelcollective/html": "5.2.*" }

2. update composer from terminal:

   composer update

3. Next, add your new provider to the providers array of config/app.php:

'providers' => [ // ... Collective\Html\HtmlServiceProvider::class, // ... ],

Finally, add two class aliases to the aliases array of config/app.php:

  'aliases' => [
    // ...
      'Form' => Collective\Html\FormFacade::class,
      'Html' => Collective\Html\HtmlFacade::class,
    // ...
  ],

the error is:

FatalErrorException in 94130ac18d8152bd785794934f1ccfb5f9a84201.php line 18: Class 'Form' not found

via Chebli Mohamed