The ornamental design for a jacket, as shown and described.
FIG. 1 is a rear perspective view of a jacket showing our new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a side view thereof;
FIG. 4 is an opposite side view thereof;
FIG. 5 is a top view thereof; and,
FIG. 6 is a front view thereof.
The broken lines immediately adjacent to the internal perimeter of the solid lines define the bounds of the claimed design and form no part thereof. The broken lines depicting the remainder of the jacket show features that form no part of the claimed design.