The ornamental design for a tray, as shown and described.
FIG. 1 is a perspective view of a tray showing my new design;
FIG. 2 is a front view thereof, the rear being a mirror image thereof;
FIG. 3 is a top view thereof; and,
FIG. 4 is a bottom view thereof.
The broken line showing is for the purpose of illustrating portions of the tray and forms no part of the claimed design.