The ornamental design for an article of apparel, as shown and described.
FIG. 1 is a front view of an article of apparel showing my new design; and,
FIG. 2 is a rear view thereof.
The broken lines showing the collar and front panel in the figs. illustrate portions of the design which are not claimed; and the broken lines shown along the edges of the front panel illustrate the boundaries of the design, which form no part of the claim.