We claim the ornamental design for a showerhead, as shown and described.
FIG. 1 is a left side perspective view of a showerhead in accordance with the present invention;
FIG. 2 is a rear perspective view of the showerhead in accordance with the present invention;
FIG. 3 is a right side elevational view of the showerhead in accordance with the present invention;
FIG. 4 is a front elevational view of the showerhead in accordance with the present invention, with the rear and right side elevational views being the mirror image thereof;
FIG. 5 is a top elevational view of the showerhead in accordance with the present invention; and,
FIG. 6 is a bottom elevational view of the showerhead in accordance with the present invention.