The ornamental design for a mirror, as shown and described.
FIG. 1 is a perspective view of an embodiment of a mirror showing our new design in a closed position;
FIG. 2 is a perspective view of the mirror in an open position;
FIG. 3 is a front view of the mirror;
FIG. 4 is a right side view of the mirror;
FIG. 5 is a left side view of the mirror;
FIG. 6 is a top plan view of the mirror; and,
FIG. 7 is a bottom plan view of the mirror.
The portions of the mirror shown in broken lines illustrate portions of the mirror that form no part of the claimed design. The remaining broken lines illustrate the environment of the claimed design and form no part thereof.