The ornamental design for a keyboard, as shown and described.
FIG. 1 is a top perspective view of a keyboard showing my new design;
FIG. 2 is a top plan view of the keyboard of FIG. 1;
FIG. 3 is an enlarged partial top plan view of the keyboard of FIG. 1;
FIG. 4 is an enlarged partial front perspective view of a key of the keyboard of FIG. 1, with a key removed for ease of illustration;
FIG. 5 is an enlarged partial top plan view of a key of the keyboard of FIG. 1, shown removed for ease of illustration;
FIG. 6 is an enlarged partial left side elevational view of a key of the keyboard of FIG. 1, with a key removed for ease of illustration;
FIG. 7 is an enlarged partial right side elevational view of a key of the keyboard of FIG. 1, with a key removed for ease of illustration; and,
FIG. 8 is an enlarged partial front elevational view of a key of the keyboard of FIG. 1, with a key removed for ease of illustration.
The broken lines depict portions of the keyboard which form no part of the claimed design.
The additional even-dash broken lines in FIGS. 1-2 are included for reference purposes in identifying enlarged, partial, detail views of a key portion of the keyboard.