Correct Junction Deviation value for Formbot Raptors

Re-apply the formula .4 * V^2 / Default_Acceleration to work correctly in Raptor configuration.h file.
(The problem is there are multiple XJerk and YJerk values declared based on the step sticks used on the printer.)
This change should provide correct values for all setups.

config/examples/Formbot/Raptor/Configuration.h

  *   http://blog.kyneticcnc.com/2018/10/computing-junction-deviation-for-marlin.html
  */
 #if DISABLED(CLASSIC_JERK)
-  #define JUNCTION_DEVIATION_MM 0.013 // (mm) Distance from real junction edge
+  #define JUNCTION_DEVIATION_MM (.4 * DEFAULT_YJERK * DEFAULT_YJERK / DEFAULT_ACCELERATION)  // (mm) Distance from real junction edge
 #endif
 
 /**