The ornamental design for a portfolio, as shown and described.
FIG. 1 is an elevational view of the design for a portfolio in accordance with the present invention; and,
FIG. 2 is a perspective view thereof.
That which is shown in the drawings comprises that which is claimed, namely, the design for a portfolio shown in the elevational view of FIG. 1. Any portion of the portfolio that is not shown in the drawings forms no part of the design for which patent protection is claimed herein. The broken lines illustrated in the drawings form no part of the design.