Need to update the scopes composer.json when installing humbug/php-scoper per docs

[JoshMoreno]

When following the docs to install locally rather than globally it says to do:

composer require --dev bamarni/composer-bin-plugin
composer bin php-scoper require --dev humbug/php-scoper

but since humbug/php-scoper has a dev-master requirement the scopes composer.json needs to be updated or it will error out on the second command. The below will is what it should be.

composer require --dev bamarni/composer-bin-plugin
composer bin php-scoper config minimum-stability dev
composer bin php-scoper config prefer-stable true 
composer bin php-scoper require --dev humbug/php-scoper

[theofidry]

Hm Indeed, would you mind opening a PR fixing it?