The ornamental design for a cushion, as shown and described.
FIG. 1 is a front view of the cushion showing my design;
FIG. 2 is a back view thereof;
FIG. 3 is a side view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a front perspective view thereof;
FIG. 7 is an enlarged view of a circled portion in FIG. 6;
FIG. 8 is a bottom perspective view thereof; and,
FIG. 9 is an enlarged view of a circled portion in FIG. 8.
A chair shown using shorter broken lines in the drawings illustrates the environment and exemplary positioning of the cushion relative to the chair, and forms no part of the claimed design. Longer dashed lines in FIGS. 6 and 8 surround portions of the figures to show where the enlarged views of FIGS. 7 and 9 were taken.