The ornamental design for a decking, as shown and described.
FIG. 1 is a front, right, top perspective view of a decking showing our new design;
FIG. 2 is a front elevational view thereof, the rear elevation view being a mirror image thereof;
FIG. 3 is a right side elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom view thereof.
The decking is shown with a symbolic break in its length. The appearance of any portion of the decking between the break lines form no part of the claimed design.