The icon it has now doesn't really blend with other native Mac apps very well. There are some nice icons on dribbble, perhaps you could get in contact with one of the designers and ask permission to use it in this app.

Here are some I like:

https://dribbble.com/shots/1854250-Trello-Icon-For-Mac
https://dribbble.com/shots/1991897-Trello-app-icon
https://dribbble.com/shots/2828143-Trello-Icon-Replacement-for-Fluid-Electron-etc-apps