The ornamental design for a tamper-proof nut, as shown and described.
FIG. 1 is a perspective view of a tamper-proof nut;
FIG. 2 is a side elevation view of the tamper-proof nut;
FIG. 3 is a front view of the tamper proof nut; and,
FIG. 4 is a rear view of the tamper-proof nut.
The design consists of the visual features of the tamper-proof nut shown in the drawings, whether those features are one of shape, configuration, ornament, or pattern or are a combination of any of these features.