FIG. 1 is a perspective view of keyboard showing our new design; FIG. 2 is a top view thereof; FIG. 3 is a bottom view thereof; FIG. 4 is a front view thereof; FIG. 5 is a back view thereof; FIG. 6 is a left view thereof; and, FIG. 7 is a right view thereof. Broken lines shown in the drawings are for environment only and form no part of the claimed design.