fix: update Requests docs link to canonical URL (#415)

The link to Requests documentation used /en/master/ which redirects
to /en/latest/. Update to the canonical URL to avoid unnecessary
redirect.

Co-authored-by: Sediman <jason@sediman.com>

README.rst

diff --git a/README.rst b/README.rst
index 7204fa6..58242e3 100644
--- a/README.rst
+++ b/README.rst
@@ -30,7 +30,7 @@
 
 Enjoy!
 
-.. _`Requests`: https://requests.readthedocs.io/en/master/
+.. _`Requests`: https://requests.readthedocs.io/en/latest/
 
 Addition/Removal of Certificates
 --------------------------------