The ornamental design for a keyboard, as shown and described.
Description:
FIG. 1 is a top front perspective view of a keyboard showing my new design;
FIG. 2 is a top view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof; and,
FIG. 5 is a front view thereof.
The broken lines in the Figures represent unclaimed portions of the design. The unshown bottom and rear portions of the keyboard form no part of the claimed design.
