I claim the ornamental design for a decoy, as shown and described.
FIG. 1 is a bottom perspective view of a decoy showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top elevation view thereof;
FIG. 7 is a bottom elevation view thereof; and,
FIG. 8 is a bottom perspective view thereof.
The broken lines depict portions of the decoy that form no part of the claimed design. The broken away symbols in the drawings indicate that any portion of the article beyond what is shown forms no part of the claimed design.