The ornamental design for a ring, as shown and described.
FIG. 1 is a front view of a ring;
FIG. 2 is a rear view thereof;
FIG. 3 is a first side view thereof;
FIG. 4 is a second side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is an enlarged perspective view of the ring worn by a user.
The broken lines showing a hand in FIG. 7 represent environment and form no part of the claimed design. The remaining broken lines in FIGS. 1-7 represent portions of the ring which form no part of the claimed design.