The ornamental design for a doll, as shown and described.
FIG. 1 is a front perspective view of a doll showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines showing the remainder of the doll represent unclaimed subject matter and form no part of the claimed design. The dot-dashed lines immediately adjacent to the shaded area represent unclaimed boundaries of the design.