The ornamental design for an inverter, as shown and described.
FIG. 1 is a perspective view from the front-top-right side of an inverter showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design while all other broken lines are for illustrative purposes only; the broken lines form no part of the claimed design.