The ornamental design for a hairbrush, as shown and described.
FIG. 1 is a front elevational view of a hair brush showing our new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a rear elevational view thereof; and,
FIG. 7 is a perspective view thereof.
The broken lines illustrate portions of the hair brush that form no part of the claimed design. In addition, the dot-dash lines illustrate boundaries between claimed and unclaimed portion of the hair brush, and form no part of the claimed design.