We claim the ornamental design for a jacket, as shown and described.
FIG. 1 is a left perspective view of a jacket, showing our new design;
FIG. 2 is a right perspective view thereof; and,
FIG. 3 is a front view thereof.
The dashed lines are included for illustrating environmental structure and the dot-dash broken lines illustrate the bounds of the claimed design. The broken lines form no part of the claimed design. The different shading/stippling is used in various regions to show contrast in appearance.