The ornamental design for a facemask, as shown and described.
FIG. 1 is a perspective view of a face mask showing the claimed design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a rear elevation view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines illustrate portions of the face mask that form no part of the claimed design. The unshaded interior surfaces of the face mask in FIGS. 1, 2 and 7 form no part of the claimed design.