The ornamental design for a planter, as shown and described.
FIG. 1 is a top isometric view of the planter of the present invention;
FIG. 2 is a front view thereof, the rear view being identical thereto;
FIG. 3 is a right side view thereof, the left side view being identical thereto;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof; and,
FIG. 6 is a bottom isometric view thereof.
The portions of the planter illustrated in broken lines form no part of the claimed design for the planter. The phantom lines provide boundaries separating the claimed and the unclaimed portions of the planter design.