The ornamental design for a sprinkler, as shown and described.
FIG. 1 is a first top perspective view of a sprinkler, according to my new design;
FIG. 2 is a second top perspective view of the sprinkler;
FIG. 3 is a first bottom perspective view of the sprinkler;
FIG. 4 is a second bottom perspective view of the sprinkler;
FIG. 5 is a front side elevational view of the sprinkler;
FIG. 6 is a rear side elevational view of the sprinkler;
FIG. 7 is a top side view of the sprinkler;
FIG. 8 is a bottom side view of the sprinkler;
FIG. 9 is a right side elevational view of the sprinkler; and,
FIG. 10 is a left side elevational view of the sprinkler.
The broken lines in the figures are included for the purpose of illustrating unclaimed portions of the sprinkler and form no part of the claimed design.