The ornamental design for a shower cap, as shown and described.
FIG. 1 is a front elevation view of the shower cap of the present design.
FIG. 2 is a rear elevation view thereof.
FIG. 3 is a left side elevation view thereof, with the right side being a mirror image thereof.
FIG. 4 is a top plan view thereof with the ears folded downward; and,
FIG. 5 is a bottom plan view thereof.
The partial human figure drawn in dash-dash broken lines is environmental subject matter included to show the shower cap in a position of use and forms no part of the claimed design. The dash-dash broken lines within the shower cap depict environmental structure that forms no part of the claimed design. The dash-dot-dash broken line shown in FIG. 5 defines the bounds of the claimed design and forms no part thereof.