The ornamental design for a charger, as shown and described.
FIG. 1 is a perspective view of a charger;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a perspective view of a charger with a cover opened to show internal elements therein.
The broken lines showing portions of the charger are included for the purpose of illustrating environmental structure and form no part of the claimed design.