The ornamental design for a massagegun, as shown and described.
FIG. 1 is a perspective view of a massage gun showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The white evenly spaced broken lines in the drawings represent portions of the massage gun that form no part of the claimed design. The black uneven dot-dash broken lines in the drawings represent a boundary line that form no part of the claimed design. The lighter shaded portions of the massage gun shown within the black uneven dot-dash boundary lines form no part of the claim design.