The ornamental design for a fastener, as shown and described.
FIG. 1 is a top, front, and right side isometric view of an ornamental design for a fastener;
FIG. 2 is a bottom, rear, and right side isometric view of the fastener of FIG. 1;
FIG. 3 is a front elevational view of the fastener of FIG. 1;
FIG. 4 is a rear elevational view of the fastener of FIG. 1;
FIG. 5 is a left side elevational view of the fastener of FIG. 1;
FIG. 6 is a right side elevational view of the fastener of FIG. 1;
FIG. 7 is a top plan view of the fastener of FIG. 1; and,
FIG. 8 is a bottom plan view of the fastener of FIG. 1.
The evenly spaced broken lines in the drawings illustrate portions of the fastener and form no part of the claimed design. The dot-dash-dot broken lines in the drawings define the bounds of the claim and form no part thereof.