I forked this repo, and added a bunch of features which I thought would make it more enjoyable and more of a challenge. I would submit each feature as a pull request, but I don't know which direction you want to take your game, so I don't want to pollute your repo with unneeded pull requests.
Check out the demo here:
https://coinminergame.herokuapp.com/
If you see any features you want ported back to the orignal game, I will happily clean up my code and do them as individual pull requests.
Thanks for making such a great game and sharing the open source code.