The ornamental design for a hat, as described and shown.
FIG. 1 is a front perspective view of a hat illustrating my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevation view thereof, the rear view being identical; and,
FIG. 4 is a left side elevation view thereof, the right side elevation view being identical thereto.
The broken line showing of a human head and hair in FIG. 1 is environmental structure only and does not form a part of the claimed design. All other broken lines represent stitching forming part of the claimed design.