New review comment by ericonr on void-packages repository

https://github.com/void-linux/void-packages/pull/28288#discussion_r569038268

Comment:
```suggestion
[ -r conf ] && . ./conf
exec 2>&1
exec wendy -m 768 -w "${SNAPSHOTS_PATH}" bash -c \
 'if [ -s "/boot/grub/grub-btrfs.cfg" ]; then /etc/grub.d/41_snapshots-btrfs; else update-grub; fi'
```