how to install vendor package from laravel package

So i'am in Laravel 5.4 and i've my custom package packages/dev/mypackage.

And i want to install soundasleep/html2text into my package, so i add this to my packages/dev/mypackage/composer.json :

{
  "require": {
    "soundasleep/html2text": "~0.5"
  }
}

then composer update , but when i tried to call html2text i got always class Html2Text\Html2Text not found.

So please if someone has any idea i'll be very appreciative.

via Chebli Mohamed