Hair Straightener

FIG. 1 is a first perspective view of a hair straightener showing my new design; FIG. 2 is a second perspective view thereof; FIG. 3 is a front view thereof; FIG. 4 is a back view thereof; FIG. 5 is a left side view thereof; FIG. 6 is a right side view thereof; FIG. 7 is a top view thereof; FIG. 8 is a bottom view thereof; and, FIG. 9 is a perspective view of another state of the hair straightener thereof. The broken lines shown in the drawings depict portions of the hair straightener that form no part of the claimed design.