The ornamental design for a tool, as shown and described.
FIG. 1 is a perspective view of a tool showing my new design;
FIG. 2 is a side view of FIG. 1, the opposite side being a mirror image;
FIG. 3 is a top view of FIG. 1;
FIG. 4 is a bottom view of FIG. 1; and,
FIG. 5 is a front view of FIG. 1.
In the drawings, the evenly-spaced broken lines represent portions of the article which form no part of the claimed design. The dot-dash broken lines represent a boundary to the claimed design and form no part thereof.