Refactor: Change 'Progress#finished?' to use instance variables
Refactor: Change 'Progress#finished?' to use instance variables

Not sure why, but we get a substantial performance boost out of using instance
variables here.  Almost an entire second on a 100,000 item bar.

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Branch:        refactor/massive-update
Signed-off-by: Jeff Felchner <8a84c204e2d4c387d61d20f7892a2bbbf0bc8ae8@thekompanee.com>

pctj101/ruby-progressbar,pctj101/ruby-progressbar