I claim the ornamental design for a scissor, as shown and described.
FIG. 1 is a front perspective view showing my new design.
FIG. 2 is rear perspective view showing my new design.
FIG. 3 is another front perspective view showing my new design.
FIG. 4 is a another rear perspective view showing my new design.
FIG. 5 is a side view showing my new design.
FIG. 6 is an opposite side view showing my new design.
FIG. 7 is a bottom view showing my new design; and,
FIG. 8 is a top view showing my new design.
The shading lines shown in the drawings represent the approximate three-dimensional contour of the design, and are not intended to indicate surface decoration.