The ornamental design for a jacket, as shown and describe.
FIG. 1 is a perspective view of a jacket showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a right side elevational view thereof, the left side elevational view being a mirror image thereof;
FIG. 5 is a bottom plan view thereof; and,
FIG. 6 is a rear elevational thereof.
The broken lines shown in protective pads embedded in shoulders and sleeves of the jacket in FIGS. 1-6 are the stitching and are part of the claimed design, and the broken lines in FIGS. 1, 2, 4, and 6 showing a body of the person wearing a jacket depict environmental subject matter only and form no part of the claimed design.