The ornamental design for a revolver, as shown and described.
FIG. 1 is a front, top, left side perspective view of a revolver showing our new design;
FIG. 2 is a rear, bottom, right side perspective view thereof;
FIG. 3 is a front, elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a left side, elevation view thereof;
FIG. 6 is a right side, elevation view thereof;
FIG. 7 is a top, plan view thereof; and,
FIG. 8 is bottom, plan view thereof.
The broken-line disclosure is understood to represent portions of the article in which the claimed design is embodied, but which form no part of the claimed design.