The ornamental design for a dehumidifier, as shown and described.
FIG. 1 is a first perspective view of a dehumidifier showing my new design;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a front view thereof,
FIG. 4 is a back view thereof,
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof,
FIG. 7 is a top view thereof,
FIG. 8 is a bottom view thereof;
FIG. 9 is an enlarged view of the selected portion 9 in FIG. 1; and,
FIG. 10 is an enlarged view of the selected portion 10 in FIG. 1.
The broken lines shown in the drawings depict portions of the dehumidifier that form no part of the claimed design. The long dash-short dash broken lines shown in FIG. 1 and FIGS. 9-10 indicate cut off boundaries for enlarged detail portion views and form no part of the claim.