The ornamental design for a hands-free umbrella, as shown and described.
FIG. 1 is a front elevation view of a hands-free umbrella showing my new design;
FIG. 2 is a rear elevation view thereof;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a top view thereof; and,
FIG. 6 is a bottom view thereof.
The broken line showing of a backpack in the figures represents environment only and forms no part of the claimed design. The portions of the umbrella shown in broken lines form no part of the claimed design.