The ornamental design for a containercap, as shown and described.
FIG. 1 is an upper front perspective view of a container cap showing our new design;
FIG. 2 is an enlarged upper front perspective view thereof;
FIG. 3 is an enlarged lower front perspective view thereof;
FIG. 4 is an enlarged front elevation view thereof, with the rear, right side, and left side elevation views being a minor image of the front elevation view; and,
FIG. 5 is an enlarged top plan view thereof.
The broken lines shown in the drawings illustrate environmental subject matter and form no part of the claimed design.