Fix obsolete link to documentation in image-to-gcode(1).

Author: petterreinholdtsen

docs/man/man1/image-to-gcode.1

@@ -33,7 +33,7 @@ image-to-gcode \- converts bitmap images to G-code
 brightness of each pixel as a Z-height. 
 
 Detailed docs:
-http://linuxcnc.org/docs/2.4/html/gui_image-to-gcode.html
+http://linuxcnc.org/docs/stable/html/gui/image-to-gcode.html
 
 .SH "SEE ALSO"
 \fBLinuxCNC(1)\fR