DOC: update Cartopy url

Author: rcomer

galleries/examples/subplots_axes_and_figures/geo_demo.py

@@ -6,7 +6,7 @@
 This shows 4 possible geographic projections.  Cartopy_ supports more
 projections.
 
-.. _Cartopy: https://scitools.org.uk/cartopy/
+.. _Cartopy: https://cartopy.readthedocs.io
 """
 
 import matplotlib.pyplot as plt