The ornamental design for a jacket, as shown and described.
FIG. 1 is a first perspective view of the jacket embodying the new design;
FIG. 2 is a second perspective view thereof; and,
FIG. 3 is a front view thereof.
FIGS. 1-3 show portions of a jacket in broken lines that do not form any part of the claimed design. Further, the broken lines immediately adjacent the solid-line portions of the design form the boundary of the design, with the broken lines forming no part of the claimed design.