Prior to this commit, the vagrantfile installs ruby 2.3.3. Due to commit mastodon@7951e7f, this no longer works. Change the provision scrip so that 2.3.1 is installed via rbenv. Note this drastically increases provision time.
The current Vagrantfile fails to build upon provisioning, as it lacks yarn. Change the Vagrantfile to add the yarn repository, and install yarn.