The ornamental design for an adapter, as shown and described.
FIG. 1 is a front perspective view thereof;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is another elevational view.
The cable portions are shown broken away with solid, cut-off lines in all the figures to indicate that no specific length is being claimed - it is understood that the interrupted portions of the cables have a uniform shape and appearance through out their length.