The ornamental design for an outsole for a shoe, as shown and described.
FIG. 1 is a bottom perspective view of an outsole for a shoe in accordance with my new design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a front view thereof; and,
FIG. 7 is a rear view thereof.
The broken lines shown in all of the figures are for environmental purposes and form no part of the claim. The broken lines shown on a face of the outsole in FIGS. 1 and 3 represent boundaries of the design with the lines themselves and the areas within them form no part of the claimed design.