The ornamental design for a cap, as shown and described.
1.1 is a top perspective view of a cap;
1.2 is a bottom perspective view thereof;
1.3 is a front view thereof;
1.4 is a right side view thereof;
1.5 is a rear view thereof;
1.6 is a left side view thereof;
1.7 is a top view thereof; and
1.8 is a bottom view thereof.
The dotted lines shown in the crown of the cap represent stitching and form part of the claimed design, except for the dotted lines shown at the eyelets in the crown of the cap which are to show environment only and form no part of the claimed design.
The bill or visor is a portion of the cap and forms no part of the claimed design.