The ornamental design for a sensor, as shown and described.
FIG. 1 is a front perspective view of a sensor showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The appearance of any portion of the sensor between the zig-zag broken lines forms no part of the claimed design. The broken line ovals within the shaded areas form no part of the claimed design. The broken lines immediately adjacent to the shaded areas represent the bounds of the claimed design and form no part thereof. The broken lines depicting the remainder of the sensor form no part of the claimed design.