Slider Bug

[billy-doyle]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of moly.

• (optional) I have confirmed this bug exists on the master branch of moly.

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Code Sample, a copy-pastable example

fig = moly.Figure()
fig.add_cube('Psi_a_9_5-A1.cube', iso=[0.03, 0.04, 0.05], plot_geometry=True)
fig.show()

Error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-29b34361b222> in <module>
      1 fig = moly.Figure()
----> 2 fig.add_cube('Psi_a_9_5-A1.cube', iso=[0.03, 0.04, 0.05], plot_geometry=True)
      3 fig.show()

~/Python_stuff/psi4labs/moly/moly/figure/figure.py in add_cube(self, file, iso, plot_geometry, colorscale, opacity, style)
    127                 self.fig.add_trace(trace)
    128 
--> 129             slider = get_slider(iso, geometry_traces)
    130             self.fig.update_layout(sliders=slider)
    131 

~/Python_stuff/psi4labs/moly/moly/figure/widgets.py in get_slider(iso, geometry_traces)
     44         one_step = {'method': "restyle", 
     45                     'label': str(iso_i),
---> 46                     'args': [{"visible": [True] * geometry_traces + [False] * len(iso)}]}
     47         one_step["args"][0]['visible'][geometry_traces + i] = True
     48         steps.append(one_step)

TypeError: can't multiply sequence by non-int of type 'tuple'

Problem description

In moly/figure/figure.py, line 120 should have the len removed.
In moly/figure/widgets.py, lines 46 and 47 do not include the len for the geometry_traces parameter.

I have tested this locally and it works as expected.

See PR #15