The ornamental design for a windscreenwiper, as shown and described.
FIG. 1 is a perspective view of a windscreen wiper showing our new design.
FIG. 2 is a front view thereof.
FIG. 3 is a rear view thereof.
FIG. 4 is a magnified left side view thereof.
FIG. 5 is a magnified right side view thereof.
FIG. 6 is a top plan view thereof.
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a cross-sectional view thereof taken along line A-A′ in FIG. 2 for purposes of illustrating a contour or configuration of the exterior surface, which may not be apparent from the other views.