I claim the ornamental design for a cap, as shown and described.
FIG. 1 is a top front left side perspective view of a cap embodying my design, with a wearer shown in phantom outline for environmental purposes and not forming any part of the claimed design;
FIG. 2 is a front elevational view of the cap of FIG. 1;
FIG. 3 is a rear elevational view of the cap of FIG. 1;
FIG. 4 is a left side elevational view of the cap of FIG. 1;
FIG. 5 is a right side elevational view of the cap of FIG. 1;
FIG. 6 is a top plan view of the cap of FIG. 1; and,
FIG. 7 is an enlarged fragmentary view of the pattern, which repeats uniformly over the cap of FIG. 1. The outline shown in phantom illustrates the bounds of the view, and forms no part of the claimed design.