Buildkit is periodically updated with newer versions of its tools. Changes are generally "drop-in" updates that don't require any special action. However, if a change requires special action, it should be documented in this changelog.
In version v14.05 (and earlier), each build included two databases: one CMS database and one Civi database. If you ran unit-tests in v14.05, the tests would reset the Civi database -- which was problematic if you like to alternate rapidly between unit-testing and manual testing (because any manual DB changes are lost).
v14.06 addresses this by provisioning a third database for testing. This requires some changes — eg creating the database, saving the metadata (eg "build/drupal-demo.sh"), and updating configs files (eg "build/drupal-demo/sites/all/modules/civicrm/tests/phpunit/CiviTest/civicrm.settings.dist.php"). You can fix all of this by reinstalling the build (which will recreate all databases and config files). If the build is named "drupal-demo", then simply run:
civibuild reinstall drupal-demo