Fix bug in example three_link_conical_pendulum

[AlainLich]

Fix bug causing error, traceback shown below.

Error: wrong argument ordering and argument keyword not used.

traceback (most recent call last):
File "/home/alain/test/physique/Sympy/Examples/three_link_conical_pendulum/visualize.py", line 9, in
from derive import I, O, links, particles, q, u
File "/home/alain/test/physique/Sympy/Examples/three_link_conical_pendulum/derive.py", line 139, in
fr, frstar = kane.kanes_equations(forces, total_system)
File "/usr/lib/python3/dist-packages/sympy/physics/mechanics/kane.py", line 543, in kanes_equations
fr = self._form_fr(loads)
File "/usr/lib/python3/dist-packages/sympy/physics/mechanics/kane.py", line 283, in _form_fr
vel_list, f_list = _f_list_parser(fl, N)
File "/usr/lib/python3/dist-packages/sympy/physics/mechanics/functions.py", line 724, in _f_list_parser
vel_list, f_list = unzip(list(flist_iter()))
File "/usr/lib/python3/dist-packages/sympy/physics/mechanics/functions.py", line 711, in flist_iter
obj, force = pair
TypeError: cannot unpack non-iterable RigidBody object

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New Feature

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[moorepants]

Thanks.