The ornamental design for a ring, as shown and described.
1. Ring
1.1 : Front
1.2 : Back
1.3 : Top
1.4 : Bottom
1.5 : Right
1.6 : Left
1.7 : Perspective
1.1 is a front view; 1.2 is a back view; 1.3 is a top view; 1.4 is a is bottom view; 1.5 is a right view; 1.6 is a left view; 1.7 is an isometric (perspective) view.