M2 spacers: 2.0mm, 2.25mm, 2.5mm, 3.0mm height

spacer for electronics stack. 2.0mm, 2.25mm, and 2.5mm heights. intended to go between bottom plate and ESC, and ESC and FC. 3.5mm outer diameter, a bit lower profile than the [pepperfiish spacer](https://www.thingiverse.com/thing:2449891).

I went with 2.25mm between bottom plate and ESC (since i'm using the racerstar star6, which has larger components compared to the tinypepper 2S), and 2.5mm between the ESC and FC.