I claim the ornamental design for a doll, as shown and described.
FIG. 1 is a front isometric view of a doll;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a top side view thereof;
FIG. 5 is a bottom view thereof; and,
FIG. 6 is a right side view thereof.
The broken lines in FIGS. 1-6 depict hair on the head portion of the doll body, and text on the arms, legs and midsection of the doll body, which form no part of the claimed design.