The ornamental design for an inverter, as shown and described.
FIG. 1 is a front view of an inverter;
FIG. 2 is a rear view thereof;
FIG. 3 is a left view thereof;
FIG. 4 is a right view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof;
FIG. 7 is a perspective view thereof;
FIG. 8 is an enlarged partial view of the area identified as 8 in FIG. 1;
FIG. 9 is an enlarged partial view of the area identified as 9 in FIG. 2; and,
FIG. 10 is an enlarged partial view of the area identified as 10 in FIG. 7.
The broken lines present in the figures, including the wording in FIGS. 1 and 8, are included for the purpose of illustrating portions of the inverter which form no part of the claimed design.