I claim the ornamental design for a target rack, as shown and described.
FIG. 1 is a left, front perspective view of the target rack showing the claimed design;
FIG. 2 is a left side elevation view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a rear elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a left, front perspective view thereof, which includes beverage containers as environment drawn with broken lines to indicate the environment forms no part of the claimed design.