Well i used this great deviantart artwork "deviant link here" and modified it to be more like current macOS icon shapes. Bettersnaptool is very nice but this makes it look more modern in the app drawer.
You can appy this by copying the image using cmd+c and then open the properties of bettersnaptool in finder---> programms and then click the icon until it gets a blue lining and then paste the new icon using cmd+v.
This is the icon i "made" :
or in high res here: