The ornamental design for a jacket, as shown and described.
FIG. 1 is a front perspective view of a jacket showing our new design;
FIG. 2 is a right side view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a front view thereof; and,
FIG. 5 is an opposite side front perspective view thereof.
The broken line immediately adjacent to the shaded area defines the bound of the claimed design and forms no part thereof. The broken lines depicting the remainder of the jacket form no part of the claimed design.