The ornamental design for a hat, as shown and described.
FIG. 1 is a perspective view of a hat showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a side view thereof; and,
FIG. 5 is a top view thereof.
The pattern depicted in phantom lines contained within the irregular shapes on the crown and the outer band of the visor form no part of the claimed design.