The ornamental design for the hobby knife, as shown and described.
FIG. 1 is a perspective view of a hobby knife showing our new design;
FIG. 2 is a side elevational view thereof, the opposite side elevational view being a mirror image thereof;
FIG. 3 is a bottom view of the hobby knife as shown in FIG. 2;
FIG. 4 is a top view of the hobby knife as shown in FIG. 2;
FIG. 5 is a front end view thereof, taken from the right of FIG. 2;
FIG. 6 is a rear end view thereof, taken from the left of FIG. 2; and,
FIG. 7 is another side elevation view thereof.
The broken line showings of the blade in FIGS. 1 through 5 and 7, and the broken line showing of the cap in FIG. 7 are included for the purpose of illustrating environmental structure and form no part of the claimed design.