We claim the ornamental design for a keyboard, as shown and described.
FIG. 1 is a top, front, right-side perspective view of a keyboard showing our new design.
FIG. 2 is a front view thereof
FIG. 3 is a front view thereof, but with the front legs omitted for ease of illustration.
FIG. 4 is a rear view thereof.
FIG. 5 is a right side view thereof.
FIG. 6 is a left side view thereof.
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design. The broken lines indicate that the areas inside of and outside of the solid line rectangles are not part of the claimed design.