Check for coverage files now uses the same algorithm as the istanbul command.

Coverage files can be located in subfolders of the root coverage folder.
See https://github.com/gotwarlost/istanbul/blob/master/lib/command/check-coverage.js#L61
Bumped version.
Updated no coverage file test to work with last fix.
Merge pull request #5 from TeamPraxis/master

Check for coverage files now uses the same algorithm as the istanbul command