The ornamental design for a swingdevice, as shown and described.
FIG. 1 is a perspective view of a swing device showing my new design.
FIG. 2 is a rear perspective view thereof.
FIG. 3 is a front view thereof.
FIG. 4 is a rear view thereof.
FIG. 5 is a left end view thereof.
FIG. 6 is a right end view thereof.
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The swing device is shown with symbolic breaks in its length. The appearance of any portion of the article between the break lines forms no part of the claimed design.