The ornamental design for a diggingdevice, as shown and described.
FIG. 1 is an isometric view of a digging device showing our new design.
FIG. 2 is a bottom perspective view thereof.
FIG. 3 is a side perspective view thereof.
FIG. 4 is a side view thereof.
FIG. 5 is a top view thereof; and,
FIG. 6 is a bottom view thereof.
The broken lines shown in the Figures illustrate portions of the digging device that form no part of the claimed design. The shade lines in the Figures show contour and do not claim surface ornamentation or treatment.