The ornamental design for a brush, as shown and described.
FIG. 1 is a top perspective view of a brush;
FIG. 2 is a bottom perspective view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a right side elevational view thereof; and,
FIG. 6 is a front elevational view thereof.
A left side elevational view is not shown because it is identical to the right side elevational view shown in FIG. 5. A rear elevational view is not shown because it is identical to the front elevational view shown in FIG. 6.
The ornamental design which is claimed is shown in solid lines in the drawings.