Update links "first_atom_number" -> "second_atom_number"

        :return: None.
        :rtype: :py:obj:`None`.

def update_atom_numbers(self):
        """Update links "first_atom_number" -> "second_atom_number"

        :return: None.
        :rtype: :py:obj:`None`.
        """
        self._ctab_data['first_atom_number'] = self.first_atom.atom_number
        self._ctab_data['second_atom_number'] = self.second_atom.atom_number