The ornamental design for a crossbow, as shown and described.
FIG. 1 is a front left perspective view of a crossbow in accordance with the present invention;
FIG. 2 is a rear right perspective view of the crossbow shown in FIG. 1;
FIG. 3 is a left side elevational view of the crossbow shown in FIG. 1;
FIG. 4 is a front elevational view of the crossbow shown in FIG. 1;
FIG. 5 is a rear elevational view of the crossbow shown in FIG. 1;
FIG. 6 is a right side elevational view of the crossbow shown in FIG. 1;
FIG. 7 is a top view of the crossbow shown in FIG. 3; and,
FIG. 8 is a bottom view of the crossbow shown in FIG. 3.
The broken lines showing mounting arrangements and additional components are for illustrative purposes only and do not form a part of the claimed design.