`m.summary()` fails on test data

[Visdoom]

m.summary()```

fails with 
```IndexError                                Traceback (most recent call last)
<ipython-input-20-0db5d921a66f> in <module>()
----> 1 m.summary()

~/Projects/MorphoPy/morphopy/_morph.py in summary(self, save_to, print_results)
    109 
    110         # node angles
--> 111         average_nodal_angle_deg, average_nodal_angle_rad, average_local_angle_deg, average_local_angle_rad = get_average_angles(self.df_paths)
    112 
    113         summary = {

~/Projects/MorphoPy/morphopy/_utils.py in get_average_angles(df_paths)
    695             nodal_angles_rad[n], nodal_angles_deg[n] = get_angle(v00, v01)
    696 
--> 697             v10 = get_local_vector(df_paths, path_ids[0])
    698             v11 = get_local_vector(df_paths, path_ids[1])
    699             local_angles_rad[n], local_angles_deg[n] = get_angle(v10, v11)

~/Projects/MorphoPy/morphopy/_utils.py in get_local_vector(df_paths, path_id)
    602 
    603     s = df_paths.loc[path_id].path[0]
--> 604     e = df_paths.loc[path_id].path[1]
    605     v= e-s
    606 

IndexError: index 1 is out of bounds for axis 0 with size 1

[Visdoom]

fixed by fixing #86