The ornamental design for a necklace, as shown and described.
FIG. 1 is a perspective view of a necklace;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right view thereof;
FIG. 5 is a left view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is a perspective view showing the necklace in an alternate curved position; and,
FIG. 9 is a perspective view, showing the necklace in an alternate curved position and worn by a person.
The broken line showing connecting magnets in FIG. 8 and broken line showing person in FIG. 9 is included for the purpose of illustrating environmental structure and forms no part of the claimed design.