The ornamental design for an eavestrough, as shown and described.
FIG. 1 is an isometric view of an eavestrough showing my new design;
FIG. 2 is a side elevation view thereof; and,
FIG. 3 is a front view thereof.
The eavestrough is shown with a symbolic break in its length. All of the break lines and the appearance of any portion of the eavestrough between the break lines form[s] no part of the claimed design.