Don't skip directories when searching for .jshintrc.

Instead of moving on to the parent directory when a .jshintrc
file was not found, the cli script was checking the
'grandparent' directory. A test was added to demonstrate the
issue / prevent regressions.

References:
    Fixes GH-850
Merge pull request #855 from mcheely/jshint-tweaks

Don't skip directories when searching for .jshintrc.