[golang-github-prometheus-client_model/f22] Bump to upstream fa8ad6fec33561be4280a8f0514318c79d7f6cb6 - related: #1190437

[Jan Chaloupka]

Summary of changes:

  ffb94f5... Bump to upstream fa8ad6fec33561be4280a8f0514318c79d7f6cb6 - (*)

(*) This commit already existed in another branch; no separate mail sent