The ornamental design for a minikeyboard, as shown and described.
FIG. 1 is perspective view of the mini keyboard showing the new design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof.
FIG. 6 is a rear view thereof; and,
FIG. 7 is a front view thereof.
The shade lines in the Figures show contour and not surface ornamentation. The broken lines in the Figures show portions of the mini keyboard which form no part of the claimed design.