Fix problems with the documentation build

This solves an issue with the build

Author: hansthen

docs/advanced_guide/polygons_from_list_of_points.md

@@ -193,7 +193,7 @@ my_envelope_map
 ```
 
 ## Concave hull (alpha shape)
-In some cases the convex hull does not yield good results - this is when the shape of the polygon should be concave instead of convex. The solution is a concave hull that is also called alpha shape. Yet, there is no ready to go, off the shelve solution for this but there are great resources (see: https://web.archive.org/web/20191207074940/http://blog.thehumangeo.com/2014/05/12/drawing-boundaries-in-python/, accessed 04.01.2019 or https://towardsdatascience.com/the-concave-hull-c649795c0f0f, accessed 29.12.2018).
+In some cases the convex hull does not yield good results - this is when the shape of the polygon should be concave instead of convex. The solution is a concave hull that is also called alpha shape. Yet, there is no ready to go, off the shelve solution for this but there are great resources (see: https://web.archive.org/web/20191207074940/http://blog.thehumangeo.com/2014/05/12/drawing-boundaries-in-python/, accessed 04.01.2019.
 
 
 ## Putting it together
@@ -265,6 +265,4 @@ my_map_global
 
 * https://medium.com/@vworri/simple-geospacial-mapping-with-geopandas-and-the-usual-suspects-77f46d40e807, accessed 29.12.2018
 
-* https://towardsdatascience.com/the-concave-hull-c649795c0f0f, accessed 29.12.2018
-
 * https://web.archive.org/web/20191207074940/http://blog.thehumangeo.com/2014/05/12/drawing-boundaries-in-python/, accessed 04.01.2019

requirements-dev.txt

@@ -32,7 +32,7 @@ pytest
 scipy
 selenium<4.27.0
 setuptools_scm
-sphinx
+sphinx==7.3.7
 types-requests
 vega_datasets
 vincent