Remove deprecated warn flag in newer Ansible command module

[flortsch]

Running this role on recent Ansible versions fails due to the usage of a deprecated/removed warn flag in the command module.

[ppacher]

Hi!

Any chance this is going to be merged soon?

[jantari]

@rdemachkovych Either this or #278 has to be merged for this role to function on ansible 2.14+

it's a very small change, if you could please accept one of the PRs?

[SuperQ]

This role has been deprecated in favor of a the prometheus-community/ansible collection.