CI issues

[edublancas]

there are a bunch of CI errors bur the process still exists successfully:

__________________________ test_plot_silhouette[png] ___________________________

args = ()
kwds = {'extension': 'png', 'request': <FixtureRequest for <Function test_plot_silhouette[png]>>}

    @wraps(func)
    def inner(*args, **kwds):
        with self._recreate_cm():
>           return func(*args, **kwds)
E           matplotlib.testing.exceptions.ImageComparisonFailure: images not close (RMS 7.666):
E           	result_images/test_clustering/silhouette_plot_six_clusters.png
E           	result_images/test_clustering/silhouette_plot_six_clusters-expected.png
E           	result_images/test_clustering/silhouette_plot_six_clusters-failed-diff.png