Python exception in curvature circle example

See here. This should've caused the test to fail (and exit with exit code 100), but it didn't, why? Fix seems straightforward though.

Traceback (most recent call last):
  File "/builds/pyddg/pyddg/ddg/visualization/blender/props.py", line 429, in update
    callback(*args, **kwargs)
  File "/builds/pyddg/pyddg/ddg/visualization/blender/props.py", line 355, in callback
    for bobj in blender_objects(*args, **kwargs):
  File "/builds/pyddg/pyddg/examples/blender/docs/tutorials_and_examples/curvature_circles.py", line 340, in blender_objects
    circles_fct(i),
  File "/builds/pyddg/pyddg/examples/blender/docs/tutorials_and_examples/curvature_circles.py", line 28, in circle
    euc_circle = ddg.geometry.spheres.sphere_from_affine_point_and_normals(c, r, n)
AttributeError: module 'ddg.geometry.spheres' has no attribute 'sphere_from_affine_point_and_normals'
File "/builds/pyddg/pyddg/ddg/visualization/blender/props.py", line 425, in update
Traceback (most recent call last):
  File "/builds/pyddg/pyddg/ddg/visualization/blender/props.py", line 429, in update
    callback(*args, **kwargs)
  File "/builds/pyddg/pyddg/ddg/visualization/blender/props.py", line 355, in callback
    for bobj in blender_objects(*args, **kwargs):
  File "/builds/pyddg/pyddg/examples/blender/docs/tutorials_and_examples/curvature_circles.py", line 340, in blender_objects
    circles_fct(i),
  File "/builds/pyddg/pyddg/examples/blender/docs/tutorials_and_examples/curvature_circles.py", line 28, in circle
    euc_circle = ddg.geometry.spheres.sphere_from_affine_point_and_normals(c, r, n)
AttributeError: module 'ddg.geometry.spheres' has no attribute 'sphere_from_affine_point_and_normals'
File "/builds/pyddg/pyddg/ddg/visualization/blender/props.py", line 425, in update
Traceback (most recent call last):
  File "/builds/pyddg/pyddg/ddg/visualization/blender/props.py", line 429, in update
    callback(*args, **kwargs)
  File "/builds/pyddg/pyddg/ddg/visualization/blender/props.py", line 355, in callback
    for bobj in blender_objects(*args, **kwargs):
  File "/builds/pyddg/pyddg/examples/blender/docs/tutorials_and_examples/curvature_circles.py", line 340, in blender_objects
    circles_fct(i),
  File "/builds/pyddg/pyddg/examples/blender/docs/tutorials_and_examples/curvature_circles.py", line 28, in circle
    euc_circle = ddg.geometry.spheres.sphere_from_affine_point_and_normals(c, r, n)
AttributeError: module 'ddg.geometry.spheres' has no attribute 'sphere_from_affine_point_and_normals'
File "/builds/pyddg/pyddg/ddg/visualization/blender/props.py", line 425, in update