text: export default function checkLine(squares, line) {
      let [a, b, c] = line;
      if (squares[a.r][a.c] &&
          squares[a.r][a.c] ===  squares[b.r][b.c] &&
          squares[a.r][a.c] === squares[c.r][c.c]
      ) {
          return squares[a.r][a.c];
      }
      return null;
  }