DOC: update Cartopy url (geopandas#3636)

Author: rcomer

doc/source/conf.py

@@ -373,8 +373,8 @@ def setup(app):
 # connect docs in other projects
 intersphinx_mapping = {
     "cartopy": (
-        "https://scitools.org.uk/cartopy/docs/latest/",
-        "https://scitools.org.uk/cartopy/docs/latest/objects.inv",
+        "https://cartopy.readthedocs.io/stable/",
+        "https://cartopy.readthedocs.io/stable/objects.inv",
     ),
     "contextily": (
         "https://contextily.readthedocs.io/en/stable/",

doc/source/gallery/cartopy_convert.ipynb

@@ -9,7 +9,7 @@
     "\n",
     "Converting between GeoPandas and CartoPy for visualizing data.\n",
     "\n",
-    "[CartoPy](http://scitools.org.uk/cartopy/) is a Python library\n",
+    "[CartoPy](https://cartopy.readthedocs.io/) is a Python library\n",
     "that specializes in creating geospatial\n",
     "visualizations. It has a slightly different way of representing\n",
     "Coordinate Reference Systems (CRS) as well as constructing plots.\n",