The ornamental design for a wheel for a stroller, as shown and described.
FIG. 1 is a perspective view of a wheel for a stroller;
FIG. 2 is a left side elevation view thereof;
FIG. 3 is another perspective view of the wheel for a stroller;
FIG. 4 is a right side elevation view thereof; and,
FIG. 5 is a left side elevation view thereof.
The broken lines in the drawings, which illustrate environmental structure or boundaries of the wheel for a stroller, do not form a part of the claimed design.