code: function (cell, counter) {
        var alphaNum = instance.utils.getCellAlphaNum(cell),
            alpha = alphaNum.alpha,
            col = instance.utils.toChar(parseInt(instance.utils.toNum(alpha) + counter, 10)),
            row = alphaNum.num;
  
        if (!col || col.length === 0) {
          col = 'A';
        }
  
        var fixedCol = alpha[0] === '$' || false,
            fixedRow = alpha[alpha.length - 1] === '$' || false;
  
        col = (fixedCol ? '$' : '') + col;
        row = (fixedRow ? '$' : '') + row;
  
        return col + '' + row;
      }
docs: change col cell index A1 -> B1 Z1 -> AA1
  @param {String} cell
  @param {Number} counter
  @returns {String}