Adding ruby 2.3.0 to the rbenv available options
Adding ruby 2.3.0 to the rbenv available options

Upgrade requested in https://trello.com/c/Q40TmMvX

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