The ornamental design for, a snowplow, as shown and described.
FIG. 1 is a front and right side view of a snowplow, showing our new design;
FIG. 2 is a rear and right side perspective view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a right side elevation view thereof; and,
FIG. 7 is a left side elevation view thereof.
In FIGS. 1-7, the broken lines are for the purpose of illustrating environmental structure for a snowplow that form no part of claimed design. In FIGS. 1-7, the gray shading does not indicate surface decoration.