Log Message:
Update ruby-progressbar to 1.8.1.

Version v1.8.1 - May 13, 2016

Fixed

* no dynamic length when working with spring

Version v1.8.0 - April 24, 2016

Added

* Gem signing via certificate
* ActiveSupport Time-Traveling Compatibility

Changed

* ProgressBar::Time to an instantiated class

Fixed

* Progress#finish causing an exception when total was unknown