The ornamental design for a mirror, as shown and described.
FIG. 1 is a front perspective view of a mirror showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a left side elevation view thereof; the right side elevation view being a mirror image thereof; and,
FIG. 4 is a top plan view thereof.
The broken lines in the figures illustrate portions of the mirror that form no part of the claimed design. Views of the mirror not shown in the figures form no part of the claimed design.