The ornamental design for a charger, as shown and described.
FIG. 1 is a top right-side perspective view of a charger showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof, the right side being a mirror image thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a perspective view thereof, shown in an environment of use.
The broken lines present in the figures are included for the purpose of illustrating portions of the article or environmental subject matter which form no part of the claimed design.