Due to recent playbook improvements and the fact that the world keeps turning, we're bumping the [version requirement for Ansible](docs/ansible.md#supported-ansible-versions) (2.4 -> 2.5).
We've also started building our own Docker image of Ansible ([devture/ansible](https://hub.docker.com/r/devture/ansible/)), which is useful for people who can't upgrade their local Ansible installation (see [Using Ansible via Docker](docs/ansible.md#using-ansible-via-docker)).