The ornamental design for a set-top box, as shown and described.
FIG. 1 is a perspective front view showing my new design of a set-top box;
FIG. 2 is a perspective rear view of the set-top box of FIG. 1;
FIG. 3 is a left side elevational view of the set-top box of FIG. 1;
FIG. 4 is a right side elevational view of the set-top box of FIG. 1;
FIG. 5 is a front elevation view of the set-top box of FIG. 1;
FIG. 6 is a rear elevation view of the set-top box of FIG. 1;
FIG. 7 is a bottom plan view of the set-top box of FIG. 1; and,
FIG. 8 is a top plan view of the set-top box of FIG. 1.
The broken lines in FIGS. 1 thru 8 of a mounting bracket, A/V and network input and output ports, and power button(s) are for the purpose of illustrating unclaimed environment of the design, are for illustrative purposes only, and form no part of the claimed design.