The ornamental design for a unicycle, as shown and described.
FIG. 1 is a front and side perspective view of a unicycle showing my new design;
FIG. 2 is a rear and side perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a side elevational view thereof from the left of FIG. 3, the side elevational view from the side opposite that shown in FIG. 4 being the mirror image thereof;
FIG. 5 is a rear elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The structure shown in broken lines is to illustrate the environment only and forms no part of the claimed design.
The pattern of lines shown on only portions of the surface of the tire is understood to continue uniformly across the entire surface of the tire.