The ornamental design for a wristwatch, as shown and described.
FIG. 1 is a perspective view of a wrist watch in accordance with my design;
FIG. 2 is a top view of a wrist watch in accordance with my design;
FIG. 3 is a bottom view of a wrist watch in accordance with my design;
FIG. 4 is a left view of a wrist watch in accordance with my design;
FIG. 5 is a right view of a wrist watch in accordance with my design;
FIG. 6 is a front elevational view of a wrist watch in accordance with my design; and,
FIG. 7 is a back elevational view of a wrist watch in accordance with my design.
The dashed broken lines show portions of the wrist watch that form no part of the claimed design. The dash-dot broken lines define the bounds of the claimed design and form no part thereof.