Set double bonds around the ring.

def format_ring_double_bond(mol):
    """Set double bonds around the ring.
    """
    mol.require("Topology")
    mol.require("ScaleAndCenter")
    for r in sorted(mol.rings, key=len, reverse=True):
        vertices = [mol.atom(n).coords for n in r]
        try:
            if geometry.is_clockwise(vertices):
                cpath = iterator.consecutive(itertools.cycle(r), 2)
            else:
                cpath = iterator.consecutive(itertools.cycle(reversed(r)), 2)
        except ValueError:
            continue
        for _ in r:
            u, v = next(cpath)
            b = mol.bond(u, v)
            if b.order == 2:
                b.type = int((u > v) == b.is_lower_first)