The ornamental design for a paverstone, as shown and described.
FIG. 1 is a perspective view of a paver stone showing my new design;
FIG. 2 is a bottom plan view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a first side view elevational view thereof;
FIG. 5 is a second side elevational view thereof;
FIG. 6 is a third side elevational view thereof; and,
FIG. 7 is a fourth side elevational view thereof.
The broken lines shown in FIG. 2 view are included for the purpose of illustrating a portion of the paver stone that forms no part of the claimed design.