Fix so-fancy#311 Windows doesn't have '\dev\null'
Fix so-fancy#311 Windows doesn't have '\dev\null'

Update DiffHighlight to use File::Spec->devnull() to avoid platform problems.

scottchiefbaker/diff-so-fancy,scottchiefbaker/diff-so-fancy,so-fancy/diff-so-fancy,so-fancy/diff-so-fancy