The ornamental design for a sneaker, as shown and described.
FIG. 1 is a perspective view of a sneaker showing my new design;
FIG. 2 is a side view thereof;
FIG. 3 is another side view thereof, opposite that of FIG. 2;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof, opposite that of FIG. 4;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines on the shoe upper depicted in the figures denote stitching and are part of the claimed design. The broken lines illustrating the shoe laces and shoe sole illustrate portions of the sneaker that form no part of the claimed design.