Class 'Collective\Html\HtmlServiceProvider' not found in laravel 5?

i currently installed laravel and trying to create my first app, however when i required the laravel collective i get error above.

here is my composer.json

{
 "require": {
    "laravel/installer": "~1.1",
    "laravelcollective/html": "5.1.*"
 }
}

and my app.php have these lines.. providers=>

 ...Illuminate\Validation\ValidationServiceProvider::class,
    Illuminate\View\ViewServiceProvider::class,
    Collective\Html\HtmlServiceProvider::class,

aliases=>

 ...'Validator' => Illuminate\Support\Facades\Validator::class,
    'View'      => Illuminate\Support\Facades\View::class,
    'Form'      => Collective\Html\FormFacade::class,
    'Html'      => Collective\Html\HtmlFacade::class,

i've been reading and searching for solutions but currently they never worked for me.. any help will be appreciated.. thanks in advance..

UPDATE this is my cmd as of now..

via Chebli Mohamed