The ornamental design for a stepstool, as shown and described.
FIG. 1 is a perspective view of one embodiment of a step stool showing my new design, the embodiment having an inset solid panel on each side thereof and an upper surface with a series of spaced, upwardly projecting, grip enhancing treads;
FIG. 2 is a front elevational view of the invention illustrated in FIG. 1, with the back elevational view being identical to the front elevational view depicted in FIG. 2;
FIG. 3 is a left elevational view of the invention illustrated in FIG. 1, with the right elevational view being identical to the left elevational view depicted in FIG. 3;
FIG. 4 is a top plan view of the invention illustrated in FIG. 1;
FIG. 5 is an enlarged perspective view of the top surface of invention illustrated in FIG. 1 particularly showing the treads thereon; and,
FIG. 6 is an enlarged perspective view of the corner of one of the legs of the invention illustrated in FIG. 1.