The ornamental design for a pacifier, as shown and described.
FIG. 1 is a front, top and right perspective view of a pacifier, showing our new design;
FIG. 2 is a front elevation thereof;
FIG. 3 is a rear elevation thereof;
FIG. 4 is a right side elevation thereof;
FIG. 5 is a left side elevation thereof;
FIG. 6 is a top plan thereof; and,
FIG. 7 is a bottom plan thereof.
In the drawings, the even-length broken lines depict portions of the pacifier that form no part of the claimed design. The dash-dot-dash broken lines in FIGS. 1 and 6 form the boundaries of the claimed design.