The ornamental design for a lightingfixture, as shown and described.
FIG. 1 is a top perspective view of a new lighting fixture;
FIG. 2 is a bottom 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 horizontal broken line appearing at the top of FIGS. 3 through 6 represents environmental structure which forms no part of the claimed design. The remaining broken line disclosures in the views represent portions of the lighting fixture which form no part of the claimed design.