The ornamental design for a lantern, as shown and described.
FIG. 1 is a front top perspective view of a lantern showing our new design;
FIG. 2 is a front bottom perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a left side elevational view thereof; and,
FIG. 7 is a top plan view thereof.
The even broken lines showing in the drawings depict portions of the lantern that form no part of the claimed design. The dot-dash broken lines depict the boundaries of the claimed design and form no part thereof.