webflo/drupal-core-require-dev provides the
require-dev dependencies of
drupal/core as a standalone package. It follows the same release cycle and versioning scheme as Drupal core. You should use the same version constraint for it as you use for Drupal core.
Drupal Core 8.7
composer require --dev webflo/drupal-core-require-dev ~8.7.0
Drupal Core 8.6
composer require --dev webflo/drupal-core-require-dev ~8.6.0