project.acquia_subname should be defined or otherwise replaced in project.yml

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Below is a snippet from the composer.json file for a BLT generated project using the default project.yml. The default project.yml should probably include an addition variable for project.description that can be used in place of project.acquia_subname, which I don't see used elsewhere in the project.

{
  "name":    "acquia/blted8",
  "license": "proprietary",
  "type":    "project",
  "description": "${project.acquia_subname}",
  "repositories": [
    {
      "type": "composer",
      "url":  "https://packagist.drupal-composer.org"
    }

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This was fixed.