Fix link to python requests documentation

docs.python-requests.org seems to be a suspended domain. The replacement link is to the same Python requests library on readthedocs.io, and points to the ssl-cert-verification section.

Author: sidshank

python/ql/src/Security/CWE-295/RequestWithoutValidation.qhelp

@@ -29,7 +29,7 @@ The example shows two unsafe calls to <a href="https://semmle.com">semmle.com</a
 
 <references>
 <li>
-Python requests documentation: <a href="http://docs.python-requests.org/en/master/user/advanced/#ssl-cert-verification">SSL Cert Verification</a>.
+Python requests documentation: <a href="https://requests.readthedocs.io/en/latest/user/advanced/#ssl-cert-verification">SSL Cert Verification</a>.
 </li>
 </references>
 </qhelp>