swapRows(row1, row2) {
                util.checkRowIndex(this, row1);
                util.checkRowIndex(this, row2);
                for (var i = 0; i < this.columns; i++) {
                    var temp = this.get(row1, i);
                    this.set(row1, i, this.get(row2, i));
                    this.set(row2, i, temp);
                }
                return this;
            }
Swaps two rows
@param {number} row1 - First row index
@param {number} row2 - Second row index
@return {Matrix} this