Modify Extruder Z-Offset

For mystic and unknown reasons the offset distance changed
from 13.5 mm to 12.4 mm.

Marlin/Configuration.h

@@ -646,7 +646,7 @@
  */
 #define X_PROBE_OFFSET_FROM_EXTRUDER 15  // X offset: -left  +right  [of the nozzle]
 #define Y_PROBE_OFFSET_FROM_EXTRUDER 15  // Y offset: -front +behind [the nozzle]
-#define Z_PROBE_OFFSET_FROM_EXTRUDER -13.5 // Z offset: -below +above  [the nozzle]
+#define Z_PROBE_OFFSET_FROM_EXTRUDER -12.4 // Z offset: -below +above  [the nozzle]
 
 // X and Y axis travel speed (mm/m) between probes
 #define XY_PROBE_SPEED 8000