The ornamental design for a downspout, as shown and described.
FIG. 1 is a top front perspective view of a downspout showing my new design.
FIG. 2 is a front view thereof.
FIG. 3 is a right side view thereof.
FIG. 4 is a left side view thereof.
FIG. 5 is a back side view thereof.
FIG. 6 is a top view thereof.
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a bottom back perspective view thereof.
The horizontal broken line in FIGS. 1 and 2 depicts a fold line that forms no part of the claimed design. The circular broken lines along the edges in FIGS. 1-8 depict portions of the downspout that form no part of the claimed design.