We claim the ornamental design for a washing machine, as shown and described.
FIG. 1 is a front perspective view of a washing machine showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left-side view thereof;
FIG. 5 is a right-side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The even broken lines in the figures depict portions of the article and form no part of the claimed design. The dot-dash broken lines in the figures represent the bounds of the design claim and form no part of the claimed design.