[#51897881] Upgrade check_graphite UNKNOWN for NaN
[#51897881] Upgrade check_graphite UNKNOWN for NaN

Upgrade `check_graphite` to pull in fix. It will now return `UNKNOWN` if the
dataset from Graphite doesn't contain any valid (non-NULL) values. This will
stop the false-positive `CRITICAL: value=NaN` alerts. Full changeset:

- https://github.com/pyr/check-graphite/compare/v0.2.0...v0.2.2

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet