Log Message:
ruby-jirametrics: update to 2.6. Changes:

- When a status can't be found, it now just dumps a warning, rather than
  blowing up. This has been a source of frustration
  for many people just starting out with the tool so we're trying to get
  some more reasonable default behaviour.
- There is a new `Issue.flow_efficiency_numbers` method that is a first
  step towards visualizing flow efficiency. Note that none of the charts
  currently make use of this.
- By default, we assume that `flagged` means blocked but not all teams use
  the flag for that purpose. Added new setting to change that behaviour:
  `settings['flagged_means_blocked'] = false`.