The ornamental design for a stringpick, as shown and described.
FIG. 1 is a perspective view of the string pick;
FIG. 2 is a front side view thereof;
FIG. 3 is a rear side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top side view thereof; and,
FIG. 7 is a bottom side view thereof.
The double jagged broken lines depicted in FIGS. 1-3 and 5-7 indicate the appearance of portions of the string of the string pick between the break lines and form no part of the claimed design.