The ornamental design for a hairdryer, as shown and described.
1. Hair dryer
1.1 : Perspective
1.2 : Front
1.3 : Back
1.4 : Top
1.5 : Bottom
1.6 : Right
1.7 : Left
The design is directed to a hair dryer; the parts shown by means of broken lines in the reproductions are not part of the claimed design; dot-and-dash lines indicate the boundary between the part of the claimed design and other parts.