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

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

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