The ornamental design for a plunger, as shown and described.
FIG. 1 is a perspective view of a plunger in accordance with an embodiment of our new design;
FIG. 2 is a side elevation view of the plunger shown in FIG. 1;
FIG. 3 is another side elevation view of the plunger shown in FIG. 1;
FIG. 4 is a top plan view of the plunger shown in FIG. 1;
FIG. 5 is a bottom plan view of the plunger shown in FIG. 1; and,
FIG. 6 is a magnified view of area 6 of the plunger identified in FIG. 2.
The dashed dot lines immediately adjacent to the shaded areas in the figures represent the boundaries of the claimed design. The dashed lines in the figures illustrate the portions of the plunger that form no part of the claimed design. None of the broken lines form any part of the claimed design.