After commit [1] scrot will no longer overwrite files unless the `-o`
option is given. This commit makes the i3lock-fancy use `scrot -z -o`
instead of just `scrot -o`.
[1]: 489e322904
When it's used from command line or as a i3 shortcut, i3lock-fancy works
without any issues. If you try to pass it as an argument to xss-lock or
xautolock running as a systemd user service, getopt and fc-match are not in
PATH and locking doesn't work as expected. This patch replaces non absolute
paths with stable ones and should fix the issue.
