Giving check in 3check does not change remaining checks

[hyperbotauthor]

I'm using your module in https://chessopsnpmts.netlify.app/ .

Select Three Check for variant, then make the moves 1. e3 d6 2. Bb5+

Remaining checks is still 3+3 in fen.

Of course this could be my app's problem, so I added a test for it in #29 .

[niklasf]

I simply forgot to implement this 🤦.

Fixed and published as v0.10.3.