We claim the ornamental design for a plug connector, as shown and described.
FIG. 1 is a top, left perspective view of a plug connector, showing our new design;
FIG. 2 is a top, right perspective view thereof;
FIG. 3 is a bottom, left perspective view thereof;
FIG. 4 is a front elevational view thereof, the rear elevational view being a mirror image;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a left side elevational view thereof; and,
FIG. 8 is a right side elevational view thereof.
The dash-dash broken lines in the figure drawings are included to show portions of the article that form no part of the claimed design. The dot-dash-dot broken lines define the bounds of the claimed design and form no part thereof.