The ornamental design for bottle cap, as shown and described.
FIG. 1 is a top plan view of my bottle cap in accordance with my new design;
FIG. 2 is a front perspective view thereof; and,
FIG. 3 is a front view thereof, with rear, left-side elevational and right side elevational views being identical.
The bottom plan view of the bottle cap is not shown in the drawings or described in the specification and, therefore, forms no part of the claimed design.
The broken lines in the figures are for illustrative purposes only and form no part of the claimed design.