I claim the ornamental design for a holder, as shown and described.
FIG. 1 is a front/left/top perspective view of a holder (front/right/top perspective view thereof would be a mirror image);
FIG. 2 is a rear/right/bottom perspective view thereof (rear/left/bottom perspective view thereof would be a mirror image);
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The uniformly broken lines represent portions of the holder that form no part of the claimed design; the dash-dot broken lines represent the bounds of the claimed design and form no part of the claimed design.