React tic-tac-toe tutorial - Rewrite Board to use two loops to make the squares instead of hardcoding them

board.jsx

  render() {
    return (
      <div>
        <div className="board-row">
          {
            Array(3).fill(null).map((_, i) => {
              const row = Array(3).fill(null).map((_, j) => this.renderSquare(3 * i + j));
              return (
                <div key={i} className="board-row">
                  {row}
                </div>
              );
            })
          }
        </div>
      </div>
    );
  }