Update rcov.rb

Hi Benjamin Fleischer, Made changes as we discussed.
Merge branch 'patch-5' of https://github.com/ff-cviradiya/metric_fu into ff-cviradiya-patch-5
[FIX] Test for #152, Divide by 0 when calculating coverage

Benjamin Fleischer, Michael Foley, pairing
Factor out Calculate utility for calculating
  integer percentages
Confirm that coverage checking is boolean

Benjamin Fleischer, Michael Foley, pairing
Merge branch 'test_percent_coverage_calculation'