The ornamental design for a wig, as shown and described.
FIG. 1 is a front perspective view of a wig.
FIG. 2 is a front elevational view of a wig.
FIG. 3 is a rear elevational view of a wig.
FIG. 4 is a left side elevational view of a wig.
FIG. 5 is a right side elevational view of a wig.
FIG. 6 is a top plan view of a wig.
FIG. 7 is a bottom plan view of a wig; and,
FIG. 8 is a front perspective view of a wig shown on a user's head.
The broken lines in drawings depicting the wide band on the outside of the wig, the inside of the wig cap and the stitches on the inside band of the wig are included for illustrating environmental elements only and form no part of the claimed design.