The ornamental design for a connector, as shown and described.
FIG. 1 is a first perspective view of my design for a connector;
FIG. 2 is a second perspective view of my design for a connector;
FIG. 3 is a third perspective view of my design for a connector;
FIG. 4 is a fourth perspective view of my design for a connector;
FIG. 5 is a bottom plan view of my design for a connector;
FIG. 6 is a top plan view of my design for a connector; and,
FIG. 7 is a left side elevational view of my design for a connector, wherein the right side elevational view is a mirror image of the left side elevational view.