The ornamental design for a pillowcover, as shown and described.
FIG. 1 is a front, right, and top perspective view of a pillow cover, showing my design.
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 shown in the drawings are included for purpose of illustrating unclaimed portions of the pillow cover and form no part of the claimed design.