added validation to check orphans dob within gestation period of fathers death

The longest and 2nd longest gestation periods are 375 days and 317 days respectively
http://www.newhealthguide.org/Longest-Pregnancy.html

Validation ensures gestation within 317 days.
If this is a constant, shouldn't it be named as: MIN_GESTATION_OFFSET

What's our stand on constant naming conventions in Ruby?