The ornamental design for a cupholder, as shown and described.
FIG. 1 is a perspective view of a cup holder showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a perspective view of the cup holder where the cup bolder is in a configuration of use.
The broken lines in FIG. 8 showing a bottle depict environment only and form no part of the claimed design. The other broken lines in the drawings depict portions of the cup holder that form no part of the claimed design.