The ornamental design for doll, as shown and described.
FIG. 1 is a front view of a first doll, showing a first new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a top view thereof; and,
FIG. 6 is a bottom view thereof.
The broken lines depicting a zipper pull and the interior of the doll's mouth are for environmental purposes only and form no part of the claimed design.