The ornamental design for a duvetcover, as shown and described.
FIG. 1 is a front isometric view of the duvet cover of the present invention;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left-side view thereof;
FIG. 6 is a top plan view thereof; and
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a front isometric detail view of FIG. 1.
The broken lines shown around the perimeter represent stitching and form part of the claimed design. The cross hatching shown indicates a fabric material only and does not represent any particular color, texture, pattern, or finish of fabric.