I assume you are running this directly from a clone of the xibosignage/xibo-cms develop repository?
If that is the case I believe it will be using the wrong base-box in Docker, which i’ve fixed but not yet merged. You can git pull https://github.com/dasgarner/xibo-cms.git bugfix/1.8.0-rc1 to get the change and then reload vagrant with vagrant reload --provision
The issue was that I was referencing the production docker container, rather than the dev - the change to the VagrantFile are here