The ornamental design for a hedge trimmer, as shown and described.
FIG. 1 is a front perspective view of a hedge trimmer;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a left side view thereof
FIG. 4 is a right side view thereof;
FIG. 5 is a front view thereof;
FIG. 6 is a rear view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines in the drawings illustrating portions of the hedge trimmer depict environmental subject matter and form no part of the claimed design.