The ornamental design for a compressor, as shown and described.
FIG. 1 is a side elevational view of a first embodiment of a compressor showing my new design, it being understood that a view from the opposite side would be a minor image of FIG. 1.
FIG. 2 is a front elevational view of the compressor of FIG. 1; and,
FIG. 3 is a rear elevational view of the compressor of FIG. 1.