I claim the ornamental design for a holder, as shown and described.
FIG. 1 is a front/left/top perspective view of a holder (a front/right/top perspective view would be a mirror image thereof), disclaimed portions that would be visible behind the transparent surfaces being omitted for a clear disclosure of the surface configuration;
FIG. 2 is a rear/right/bottom perspective view thereof (a rear/left/bottom perspective view would be a mirror image thereof);
FIG. 3 is a front elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a top plan view thereof, disclaimed portions that would be visible behind the transparent surfaces being omitted for a clear disclosure of the surface configuration; and,
FIG. 6 is a bottom plan view thereof.
The broken lines show portions of the holder that form no part of the claimed design.