Mask

FIG. 1 is a front view of a mask showing my new design;

FIG. 2 is a rear view thereof;

FIG. 3 is a left side view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines in the figures illustrate portions of the mask that form no part of the claimed design.