The ornamental design for a towel, as shown and described.
FIG. 1 is an enlarged fragmentary top plan view of a towel, showing my new design; and,
FIG. 2 is a top plan view thereof.
Depth of the article forms no part of the claimed design.
The dash-dash broken lines shown in FIG. 2 represent the boundaries and stitching which form no part of the claimed design. The towel is shown with a symbolic break in its width. The appearance of any portion of the article between the long dash-dot-dot-dash break lines of FIG. 2 form no part of the design.