FIG. 1 is a perspective view of a showerhead showing our new design; FIG. 2 is a front face view thereof; FIG. 3 is a rear view thereof; FIG. 4 is a top plan view thereof, the opposite side being a mirror image of the side shown; and, FIG. 5 is a right side view thereof, the opposite side being a mirror image of the side shown. The broken line showing is included for the purpose of illustrating and forms no part of the claimed design.