We claim the ornamental design for a refrigerator door, as shown and described.
FIG. 1 is the front perspective view of a refrigerator door showing our new design;
FIG. 2 is the front view thereof;
FIG. 3 is the rear view thereof;
FIG. 4 is the left-side view thereof;
FIG. 5 is the right-side view thereof;
FIG. 6 is the top plan view thereof; and,
FIG. 7 is the bottom plan view thereof.
The broken lines depict portions of the refrigerator door that form no part of the claimed design. The dot-dash lines in the figures represent an unclaimed boundary line and form no part of the claimed design.