Tests: Fix inequivalent spec

The issue with this change is that the spec was starting the bar at `0` and then
making an expectation about the running average and then starting the bar
_again_ and making an expectation.

Obviously the fact that the bar is started and then started again, is logically
different than a bar that is started and then has an amount of progress set on
it.

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Change-Id:     I482e9543ff42f2dc10d468deb1d9f529caf236be
Signed-off-by: Jeff Felchner <accounts+git@thekompanee.com>
Feature: The running average is always set back to 0 when the bar is reset

Previously when the bar was reset or restarted, the running average would not
also be reset.  Additionally if the bar was started at some arbitrary point in
the middle of progress, it should not have a running average at that point.

This change (by referencing progress made) rather than total progress, fixes
both issues.

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Github Issue URLs:
  * https://github.com/jfelchner/ruby-progressbar/issues/66
Actions:
  * Closes #66
Branch:        feature/fix-running-average-when-bar-is-reset
Change-Id:     I211e53846faa784b78667c956f449148539ca458
Signed-off-by: Jeff Felchner <accounts+git@thekompanee.com>
Merge branch 'feature/fix-running-average-when-bar-is-reset-closes-66'