The ornamental design for a hairretainer, as shown and described.
FIG. 1 is a perspective view of the hair retainer of the present invention;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a side elevational view thereof;
FIG. 4 is a bottom plan view thereof; and,
FIG. 5 is a rear elevational view thereof.
The broken line showing the woman's head in FIG. 1 is illustrative of environmental structure only and forms no part of the claimed design. The broken lines in FIGS. 1, 2 and 5 that show an elongated rectangle and four “X”'s represent conventional stitching.