The ornamental design for a flashlight, as shown and described.
FIG. 1 is a perspective view of a flashlight showing my new design, with the broken line showing for illustrative purposes only and forming no part of the claimed design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a perspective view thereof wherein the cap is in an open position; and,
FIG. 4 is a side elevational view thereof, the opposite side being substantially identical.