cronie: explicitly specify vi path
This bug resulted in crontab -e failing when $EDITOR was not set because the configure script detected vi path from the host system which is probably /usr/bin/vi, but OpenWrt has vi in /bin/vi
This MR fixes the issue from #803 (closed), but that issue has two parts - vi path being wrong (fixed by this PR) and a suggestion to set $EDITOR in environment - build!469 (closed). Both of these MRs fix the same issue, but are independent.