The ornamental design for a spanner, as shown and described.
FIG. 1 is perspective view of the spanner of this invention;
FIG. 2 is a top plan view of the spanner of FIG. 1 showing the top surface of the spanner, with the opposing bottom view being the mirror image thereof and showing the bottom surface of the spanner;
FIG. 3 is a front plan view of the spanner of FIG. 1; and,
FIG. 4 is a back plan view of the spanner of FIG. 1.