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;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a left side view thereof showing the doll in another position.
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.