rather than rely on just waiting for 1 second, use sync to ensure
that copying the generated gcode to the sd card is complete before
unmounting it. this will most of the time be quicker than 1 second,
but also will be longer if necessary.
%-makerfarm.print: %-makerfarm.gcode
cp $< /media/${USER}/3D-PRINTER
%-makerfarm.print: %-makerfarm.gcode
cp $< /media/${USER}/3D-PRINTER
umount /media/${USER}/3D-PRINTER
%-materia-101.gcode: %.stl materia-101.ini
umount /media/${USER}/3D-PRINTER
%-materia-101.gcode: %.stl materia-101.ini