The ornamental design for a lavatory, as shown and described.
FIG. 1 is a left, top, front perspective view of a lavatory in the form of a movable bowl with an open bottom and of a receptor for receiving water from the bowl;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevational view thereof, the rear elevational view being identical to the front elevational view shown; and,
FIG. 4 is a left side elevational view thereof, the right side elevational view being a mirror image of the left side shown.