Servo lower cover

I have added 4 drills to the servo lower cover so that it is more symmetric.This improvement allows the servos to be easily screwed to other parts. The process of building articulated robots is now easier as well.

Github repository:
https://github.com/Obijuan/3D-parts/tree/master/Servo_lower_cover

More information (in Spanish) can be found in this link: http://www.iearobotics.com/wiki/index.php?title=Tapas_inferiores_para_Servos