The ornamental design for a robot, as shown and described.
FIG. 1 is a perspective view of a robot;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a side elevational view thereof, the right and left side views being mirror images of each other; and,
FIG. 5 is a top plan view thereof.
The broken line showing of arms and legs in FIGS. 1-5 is for the purpose of illustrating portions of the environmental structure and forms no part of the claimed design. Portions of the body and head of the robot shown in broken lines in FIGS. 1-4 do not form part of the claimed design.