The ornamental design for a jacket, as shown and described.
FIG. 1 is a right, front perspective view of a jacket according to the present design;
FIG. 2 is a front view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a back view thereof; and,
FIG. 5 is a top-down view thereof.
The evenly spaced broken lines shown in the drawings depict portions of the article that from no part of the claim. The dash-dot broken lines depict boundaries of the claimed design that form no part of the claim.