Remove stale document link

Author: hansthen

docs/advanced_guide/polygons_from_list_of_points.md

@@ -193,7 +193,7 @@ my_envelope_map
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 ## 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