Fixing composer path for scaffolding

[stevector-streaming]

This change fixes the bug described in #38 although it seems oddly cumbersome to figure out the DRUPAL_ROOT and then go up a directory. I would expect there's a more straightforward way to determine the root composer.json.

I tested this change in a personal D11 project by:

Registering the fork at the root composer.json

composer config repositories.drupal-integrations vcs [email protected]:stevector-streaming/drupal-integrations.git

I updated the requirement to use the branch

composer require "pantheon-systems/drupal-integrations:dev-patch-1@dev"

And then I ran the command successfully

ddev drush ev '\Pantheon\Integrations\Utils::stopScaffolding();'

[stevector]

@greg-1-anderson can you review/merge this one?