I claim the ornamental design for the eraser, as shown and described.
FIG. 1 is a perspective view of the eraser;
FIG. 2 is a side view of the eraser;
FIG. 3 is a rear view of the eraser;
FIG. 4 is a front view of the eraser;
FIG. 5 is a top view of the eraser; and,
FIG. 6 is a bottom view of the eraser.
The broken lines showing the inside of the four circles on the handle in FIG. 2 are included for the purpose of illustrating environment and form no part of the claimed design.