Modified Mold for EggBot

I have been using the [silicone molds for Egg Painter Mini posted by @ANicolai](https://www.thingiverse.com/thing:2673317) but I noticed that the marker hits the edge of the larger pad when it gets close to that end. To solve that problem, I trimmed the edge of the pad down at an angle with an X-acto knife and it worked much better. So... to that end, I have recreated mold_a with a built in bevel. While I was at it, I added a curve to the indention to help grip the egg better than the flat did.