I claim the ornamental design for a jacket, as shown and described.
FIG. 1 is a back right perspective view of a jacket, showing my new design;
FIG. 2 is a back left perspective view thereof; and,
FIG. 3 is a back view thereof.
The regular dot-dash lines are included for the purpose of illustrating portions of the jacket that form no part of the claimed design. The bold dot-dash lines represent boundaries of the claimed design. The contrast of shading/stippling used in various regions represents a difference in appearance either by color, texture, material and/or finish.