The ornamental design for a lightingfixture, as shown and described.
FIG. 1 is a bottom perspective view of a new lighting fixture;
FIG. 2 is a top 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. 3-9 represent environment which forms no part of the claimed design. The remaining broken line disclosures in the Figures represent portions of the lighting fixture which form no part of the claimed design.