The ornamental design for a cupholder, as shown and described.
FIG. 1 is a perspective view of a first embodiment of a cup holder showing the new design;
FIG. 2 is a right side view thereof, the left side view being a mirror image thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top view thereof; and,
FIG. 6 is a bottom view thereof.
The surface shading illustrated in the drawings is provided merely to highlight the contour of design; it is not intended to be illustrative of texture or gloss.