The ornamental design for a bucket, as shown and described.
FIG. 1 is a front left perspective view of a bucket that shows my new design;
FIG. 2 is a front view, the opposite side being a mirror image thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a side view, the opposite side being a mirror image thereof;
FIG. 5 is a bottom view thereof; and,
FIG. 6 is a bottom right perspective view thereof.
The even broken lines immediately adjacent to the shaded area represent unclaimed boundaries of the design. The even broken lines are for illustrative purposes only and form no part of the claimed design.