The ornamental design for a keycap, as shown and described.
FIG. 1 is a perspective view of a key cap showing my new design;
FIG. 2 is a front view thereof, the rear view being identical to the front view;
FIG. 3 is a left side view thereof, the right side view being identical to the left side view;
FIG. 4 is a top view thereof; and,
FIG. 5 is a bottom view thereof.
The broken lines shown in FIGS. 1-4 that are immediately adjacent to the shaded areas represent the bounds of the claimed design, while all other lines are directed to environment and form no part of the claimed design, and the broken lines shown in FIG. 5 are for illustrative purposes only and do not form part of the claimed design.