We claim the ornamental design for the double-sprocket bicycle adapter, as shown and described.
FIG. 1 is a perspective view of a double-sprocket bicycle adapter showing the new design.
FIG. 2 is right side elevation view of a double-sprocket bicycle adapter showing the new design with the left side elevation view being a mirror-image thereof.
FIG. 3 is top plan view of the double-sprocket bicycle adapter showing the new design.
FIG. 4 is a front elevation view of a double-sprocket bicycle adapter showing the new design; and,
FIG. 5 is a bottom plan view of the double-sprocket bicycle adapter showing the new design.