Ansible 2.5.4 not supported by Python 3.8+ on Mac

[GShuttleworth]

Some ansible playbooks won't run on Mac using Python 3.8.

This is solved by bumping the ansible version specified in requirements.txt to a modern version.

ansible-playbook ansible-03-netconf-config/03-ntp_create.yaml

PLAY [NETCONF create NTP server] ***********************************************

TASK [set_fact] ****************************************************************
ERROR! Unexpected Exception, this is probably a bug: cannot pickle '_io.TextIOWrapper' object