DEPRECATION WARNING stops installation

Hello, I'm trying to setup a local Dockos instance by following the instructions here: https://doc.dokos.io/dokos/setting-up/.

My Vagrantfile is:

Vagrant.configure("2") do |config|
    config.vm.box = "generic/ubuntu1804"
    config.vm.define "vagrant"
    config.vm.network "private_network", ip: "192.168.15.162"
end

and I've run:

adduser dokos
usermod -aG sudo dokos
su - dokos
wget https://gitlab.com/dokos/docli/raw/master/playbooks/install.py
export LC_ALL=C.UTF-8
sudo python3 install.py --production --user dokos

and my logs are as follows:

Checking System Compatibility...
ubuntu 18 is compatible!
Extracting templates from packages: 100%
curl already installed!
wget already installed!
git already installed!
Installing pip3...
pip3 installed!
 [WARNING]: No inventory was parsed, only implicit localhost is available
 [WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'
Input MySQL and Frappe Administrator passwords:
Please enter mysql root password: 
Re-enter mysql root password: 
Please enter the default Administrator user password: 
Re-enter Administrator password: 
Passwords saved at ~/passwords.txt
 [WARNING]: No inventory was parsed, only implicit localhost is available
 [WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'
 [WARNING]: Could not find aptitude. Using apt-get instead
 [WARNING]: Consider using the get_url or uri module rather than running 'curl'.  If you need to use command because get_url or uri is insufficient you can add 'warn: false' to this command task or set
'command_warnings=False' in ansible.cfg to get rid of this message.
[DEPRECATION WARNING]: Use errors="ignore" instead of skip. This feature will be removed in version 2.12. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.
Traceback (most recent call last):
  File "install.py", line 422, in <module>
    install_bench(args)
  File "install.py", line 221, in install_bench
    run_playbook('site.yml', sudo=True, extra_vars=extra_vars)
  File "install.py", line 339, in run_playbook
    success = subprocess.check_call(args, cwd=os.path.join(cwd, 'playbooks'), stdout=log_stream, stderr=sys.stderr)
  File "/usr/lib/python3.6/subprocess.py", line 311, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['ansible-playbook', '-c', 'local', 'site.yml', '-vvvv', '-e', '@/tmp/extra_vars.json', '--become', '--become-user=dokos']' returned non-zero exit status 2.

What am I doing wrong?