The ornamental design for a flashlight, as shown and described.
FIG. 1 is a perspective-view of my new design;
FIG. 2 is a right side view thereof, the left side view thereof being a mirror image;
FIG. 3 is a rear elevational view thereof; and,
FIG. 4 is a front elevational view thereof.
The broken line showing of the lighting end is for illustration purposes only and forms no part of the claimed design.