Ignore maxErrors when NaN

For some reason, in some of the grunt-jscs tests, `maxErrors` option was passed as `NaN`.
This resulted in failure of the tests (because the error list was being cut to 0) and the delay
in releasing a new version depending in jscs@1.7.0.

I don't know if I should have invested more time in trying to fix this problem in grunt-jscs, but
right now is 3h12 AM here in Brazil, and I'm tired as hell :(
All I wanted to do is fix these errors so a new release of grunt-jscs could be made :D