The ornamental design for a humidifier, as shown and described.
FIG. 1 is a front perspective view of a humidifier;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a right elevation view thereof;
FIG. 5 is a left elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines showing stars illustrate patterns on the translucent sleeve and form no part of the claimed design. The remaining broken lines in the figures illustrate the portions of the design that form no part of the claimed design. None of the broken lines form any part of the claimed design.
The characteristic feature of the design resides in the shape of the humidifier and an outer translucent sleeve.