Update a project installed via composer_manager or drush to a CI based Composer template under Drupal VM
If you have to go for a Drupal core update from a previous install based on composer_manager or drush (both deprecated), consider installing something robust, Composer friendly, that excludes vendor and core for a lightweight repository and enables CI and automation tools like Phing, Behat, PHPUnit, CodeSniffer, ...
If you don't have Drupal VM installed, head to the documentation.