factory_girl gem is deprecated, please upgrade to factory_bot
See https://github.com/thoughtbot/factory_bot/blob/v4.9.0/UPGRADE_FROM_FACTORY_GIRL.md for further instructions.
This needs introducing 'factory_bot' in Debian. Therefore, please wait before making this change up until I've done the Debian part, which might take a while, as a backport is needed as well. I doubt that this will happen before the end of the year, so let's do this in spring 2018.