FIG. 1 is a left front perspective view of our design for a compressor; FIG. 2 is a left side elevation view thereof; FIG. 3 is a front view thereof; FIG. 4 is a right side view thereof; FIG. 5 is a rear elevation view thereof; FIG. 6 is a top plan view thereof; and, FIG. 7 is a right rear perspective view thereof.