The ornamental design for a gate hinge, as shown and described.
FIG. 1 is a top, front, and right side perspective view of a gate hinge according to my new design, the top, front, and left side perspective view being a mirror image thereof;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines depict portions of the gate hinge that form no part of the claimed design.