The ornamental design for an expandableshelf, as shown and described.
FIG. 1 is a perspective view of the expandable shelf in a retracted configuration;
FIG. 2 is a perspective view of the expandable shelf in an expanded configuration;
FIG. 3 is a front elevational view of the expandable shelf in the retracted configuration;
FIG. 4 is a rear elevational view of the expandable shelf in the retracted configuration;
FIG. 5 is a left side elevational view of the expandable shelf in both the retracted and the expanded configurations, the opposite side of which is an identical mirror image;
FIG. 6 is a top plan view of the expandable shelf in the retracted configuration; and,
FIG. 7 is a bottom plan view of the expandable shelf in the retracted configuration.
The features shown in broken lines form no part of the claimed design.