Log Message:
ruby-jirametrics: update to 2.3. Changes:

- Renamed story_point_accuracy_chart to estimate_accuracy_chart to more
  accurately capture what it does; it's not just story points. The old
  name will continue to work for now but has been deprecated and you'll
  get a warning.
- Explicitly force all files to be loaded in UTF-8 to fix bug #27
  happening on JRuby.