Anet A8 - Z endstop switch holder

[Alexan9er's Z endstop](https://www.thingiverse.com/thing:2008349) is a great design. This is a remix of its switch holder (`z-endstop-holder.stl`).

As suggested by Alexan9er, I removed the metal lever from the switch. Then, I had to modify the switch holder for a better alignment with the screw and its cap.