The ornamental design for a flashlight, as shown and described.
FIG. 1 is a perspective view of my design;
FIG. 2 is a front view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a back view thereof; and,
FIG. 6 is a top view thereof.
The oblique lines on the lens of my design (as visible in FIGS. 1 and 6) indicate that it is at least translucent and may be transparent. The dashed lines in the figures form no part of the claimed design. All other surface(s) or portion(s) of my flashlight not shown in the figures or otherwise described in the specification, such as the bottom thereof and such as the location behind the lens, form no part of the claimed design.