Check if file exists to avoid trying to delete a non-existent file. Fixes GH-23.
Check if file exists to avoid trying to delete a non-existent file. Fixes GH-23.

adjohnson916/grunt-contrib-clean,Drooids/grunt-contrib-clean,lkiarest/grunt-contrib-clean,boostermedia/grunt-clean-alt,gruntjs/grunt-contrib-clean,nqdy666/grunt-contrib-clean