The ornamental design for a screwdriver, as shown and described.
FIG. 1 is a front perspective view of a screwdriver according to the present invention;
FIG. 2 is a left side view of the screwdriver of FIG. 1;
FIG. 3 is a right side view of the screwdriver of FIG. 1;
FIG. 4 is a top view of the screwdriver of FIG. 1;
FIG. 5 is a bottom view of the screwdriver of FIG. 1;
FIG. 6 is a front view of the screwdriver of FIG. 1; and,
FIG. 7 is a rear view of the screwdriver of FIG. 1.
The broken lines in the figures merely illustrate the environment for the screwdriver of the present design and therefore form no part of the claimed design.