Bump Ansible version_tested_max to 2.4.2.0

[fullyint]

In my tests, Trellis works with Ansible 2.4.2.0 as expected.

The only exception is that the Trellis output.py callback plugin was not formatting failure output as expected (e.g., not interpreting \n line breaks). The plugin had been triggering such formatting when the failed: True status appeared in the result formerly sent to callbacks.

Such statuses were removed in ansible/ansible#27175, the rationale being that "statuses are already reflected on the event type." For example, the v2_runner_on_failed event obviously implies failed status. The Trellis output plugin was already loading and passing along a task_failed attribute that can serve just as well.

Before fix

TASK [connection : Warn about change in host keys] **************************************************************************
System info:
  Ansible 2.4.2.0; Darwin
  Trellis at "Add MariaDB 10.2 PPA"
---------------------------------------------------
fatal: [example.com]: FAILED! => {"changed": false, "msg": "WARNING: REMOTE HOST IDENTIFICATION HAS
CHANGED!\n\nIf this change in host keys is expected (e.g., if you rebuilt the server\nor if the
Trellis sshd role made changes recently), then run the following\ncommand to clear the old host key
from your known_hosts.\n\n  ssh-keygen -R example.com\n\nThen try your Trellis playbook or SSH 
connection again.\n\nIf the change is unexpected, cautiously consider why the host 
identification\nmay have changed and whether you may be victim to a man-in-the-middle attack.

After fix

TASK [connection : Warn about change in host keys] **************************************************************************
System info:
  Ansible 2.4.2.0; Darwin
  Trellis at "Bump Ansible `version_tested_max` to 2.4.2.0"
---------------------------------------------------
WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!

If this change in host keys is expected (e.g., if you rebuilt the server
or if the Trellis sshd role made changes recently), then run the following
command to clear the old host key from your known_hosts.

  ssh-keygen -R example.com

Then try your Trellis playbook or SSH connection again.

If the change is unexpected, cautiously consider why the host identification
may have changed and whether you may be victim to a man-in-the-middle attack.