Updated ffish.js to 0.6.0

Updated ffish.js to 0.6.0
* made validate_fen() more robust (allows '-' for variants which do not
have no-progress counter or castling rights)
* added is_move_none() check to board.push(), board.push_san(),
board.san_move(), board.variation_san()
* added board.variant()
* bug fix: Added ++curIdx after parsing comment in read_game_pgn()
* ffish.js supports now "atomic" as it has been integrated into Fairy-
Stockfish