We claim the ornamental design for a cushion, as shown and described.
FIG. 1 shows an upper perspective view of the cushion;
FIG. 2 shows a top plan view thereof (the bottom view being the same);
FIG. 3 shows a front elevational view thereof (the rear elevational view being the same);
FIG. 4 shows a right end elevational view thereof (the left end view being the same);
FIG. 5 shows an example of the cushion in a mattress environment; and,
FIG. 6 shows an example of the cushion in a pillow environment.
The details shown in broken lines form no part of the claimed design. The cushion is shown with a symbolic break in its length (as designated by the bracket). The appearance of any portion of the article between the break lines forms no part of the claimed design.