Trebuchet Base (remix from JSpauld)

This is a very small remix of the base from the trebuchet that jspauld did. The channel that holds the payload is designed in a 'v', which is pretty hard to print since there is just one line of filament that represents the base. I added a box around the 'v' in Tinkercad to provide a 10mm base. There are no other changes.