The ornamental design for a backscratcher, as shown and described.
FIG. 1 is a perspective view, from above, of a backscratcher showing my new design. A perspective view from below is a mirror image thereof; and,
FIG. 2 is a perspective view, from above, of the backscratcher of FIG. 1, but with the parts shown in a folded position. A perspective view from below is a mirror image thereof.