The ornamental design for a stylus, as shown and described.
FIG. 1 is a perspective view of a stylus showing our new design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a front view thereof;
FIG. 7 is a rear view thereof;
FIG. 8 is an enlarged view of the encircled portion labeled as 8 in FIG. 2; and,
FIG. 9 is an enlarged view of the encircled portion labeled as 9 in FIG. 2.
The broken lines showing of the encircled portions in FIGS. 2, 8, and 9 form no part of the claimed design. The difference in surface shading indicates a contrast of appearance and does not depict any particular color, texture, or material.