The ornamental design for a hedge trimmer, as shown and described.
FIG. 1 is a perspective view of a hedge trimmer showing my new design;
FIG. 2 is a front view thereof
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line showing of the hedge trimmer is included for the purpose of illustrating portions of the article and forms no part of the claimed design.