update flask documentation URL

Author: dcrosta

README.md

@@ -22,4 +22,4 @@ def home_page():
 
 * [Flask-PyMongo Documentation](https://flask-pymongo.readthedocs.org/)
 * [PyMongo Documentation](https://pymongo.readthedocs.io/en/stable/)
-* [Flask Documentation](https://flask.pocoo.org/docs/)
+* [Flask Documentation](https://flask.palletsprojects.com/)

docs/conf.py

@@ -256,6 +256,6 @@
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {
     "python": ("https://docs.python.org/", None),
-    "flask": ("https://flask.pocoo.org/docs/", None),
+    "flask": ("https://flask.palletsprojects.com/", None),
     "pymongo": ("https://pymongo.readthedocs.io/en/stable/", None),
 }