The ornamental design for a towel, as shown and described.
FIG. 1 is a perspective view of a towel, showing my new design in use;
FIG. 2 is a rear view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a left side view thereof; and,
FIG. 8 is a left side view thereof; showing a pocket in an unzipped position.
The broken lines in FIG. 1, showing portions of the human figure, illustrate the design in use and form no part of the claimed design. The remaining broken lines, in FIGS. 1-3, represent the portions of the towel, which form no part of the claimed design.