should_use_book(): unexpected ply count

[lucasart]

For example if depth=0, white gets one book move, black none. Should be < not <=.

In fact it's very confusing to use plies instead of full moves which is what most users expect. I can't see a reason for using an odd number

[Heiaha]

Sure, makes enough sense. Updated in https://github.com/Heiaha/asyncLio-bot/commit/f82d45fbd8881401bf0fa812f2f5629a0d8292ec.