The ornamental design for a percussioninstrument, as shown and described.
FIG. 1 is a front perspective view of a percussion instrument;
FIG. 2 is a front view thereof;
FIG. 3 is a back side view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a first side view thereof; and,
FIG. 7 is a second side view thereof.
The broken lines in the figures are included for the purpose of illustrating a portion of the percussion instrument that forms no part of the claimed design.