The ornamental design for a lightingfixture, as shown and described.
FIG. 1 is a bottom, front, right perspective view of a lighting fixture showing my new design;
FIG. 2 is a bottom view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a rear view thereof; and,
FIG. 7 is a left side view thereof.
The broken lines immediately adjacent to the shaded area represent unclaimed boundaries of the design. The broken lines showing the remainder of the lighting fixture are for environmental purposes only and form no part of the claimed design.