The ornamental design for a rainwatercollector, as shown and described.
FIG. 1 is an isometric view of the rainwater collector;
FIG. 2 is an elevation view of a first side thereof;
FIG. 3 is a front view thereof;
FIG. 4 is an elevation view of a second side thereof; and,
FIG. 5 is a top view thereof.
Views of the bottom side and the back side of the rainwater collector have been omitted because such sides are flat and devoid of surface ornamentation.
The broken lines in FIG. 1 are for the purpose of illustrating environment and form no part of the claimed design.