Tuto-GUDHI-DTM-filtrations.ipynb: axes handle is not correct

[VincentRouvreau]

With gudhi 3.1.0, the axes shall not be handled this way:

' Usual Rips complex on X '
st_rips = gudhi.RipsComplex(X).create_simplex_tree(max_dimension=2) # create a Rips complex     
diagram_rips = st_rips.persistence()                                # compute the persistence

# plot the persistence diagram
fig, ax = plt.subplots()
gudhi.plot_persistence_diagram(diagram_rips)                    
ax.set_title('Persistence diagram of the Rips complex')

It is better to do:

# plot the persistence diagram
gudhi.plot_persistence_diagram(diagram_rips)                    
plt.title('Persistence diagram of the Rips complex')

For axes management, cf. persistence density documentation