I claim the ornamental design for an article of furniture, as shown and described.
FIG. 1 shows a perspective view of an article of furniture;
FIG. 2 is a front elevation view of the article of furniture;
FIG. 3 is left side view of the article of furniture, the right side view being a mirror image of the left side; and,
FIG. 4 is a top plan view of the article of furniture.
The bottom of the article of furniture is flat and unornamented. The broken lines are for illustrative purposes only and form no part of the claimed design.