FIG. 1 is a front perspective view of a brush showing my new design. FIG. 2 is a top plan view thereof. FIG. 3 is a right side elevation view, the left side being a mirror image thereof. FIG. 4 is a bottom plan view thereof. FIG. 5 is a front elevation view thereof; and, FIG. 6 is a rear elevation view thereof. The broken lines in the figures are for illustrative purposes only and form no part of the claimed design.