The ornamental design for a humidifier, as shown and described.
FIG. 1 is a front elevational view of a humidifier showing my new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a perspective view thereof.
The dashed lines immediately adjacent to the claimed outside perimeter of the bottom of the base in FIG. 6 represent the boundaries of the claimed design. The dashed 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.