The ornamental design for a scissor, as shown and described.
FIG. 1 is a perspective view of a scissor, showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is rear front view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is another perspective view thereof.
The evenly-spaced broken lines in the drawings illustrate portions of the scissor which form no part of the claimed design. The unevenly-spaced broken lines illustrate the bounds of the claimed design and form no part thereof.