Minor, fix spelling in man page

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

light.1

 .Nm
 caches settings and current brightness in
 .Pa /etc/light .
-In its non-priviliged mode of operation the
+In its non-privileged mode of operation the
 .Pa ~/.cache/light
 directory is used instead.
 .Sh AUTHORS