We claim the ornamental design for a sensor, as shown and described.
FIG. 1 is an isometric right side, rear view of a sensor;
FIG. 2 is an isometric right side, top view thereof;
FIG. 3 is an isometric front, top view thereof;
FIG. 4 is an isometric rear, top view thereof; and,
FIG. 5 is an isometric bottom, left side view thereof.
The broken line showing of structural features is included for the purpose of illustrating non-claimed subject matter and forms no part of the claimed design.