The ornamental design for a lightingfixture, as shown and described.
FIG. 1 is a front perspective view of a lighting fixture depicting a new design;
FIG. 2. is a back perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a back elevational view thereof;
FIG. 5 is a left elevational view thereof;
FIG. 6 is a right elevational view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines extending from the lighting fixture in FIGS. 5 through 8 represent environment which forms no part of the claimed design. The remaining broken line disclosures in the views represent portions of the lighting fixture that form no part of the claimed designs.