Bump cryptography from 3.4.8 to 39.0.1 in /docs

Bumps [cryptography](https://github.com/pyca/cryptography) from 3.4.8 to 39.0.1.
- [Release notes](https://github.com/pyca/cryptography/releases)
- [Changelog](https://github.com/pyca/cryptography/blob/main/CHANGELOG.rst)
- [Commits](pyca/cryptography@3.4.8...39.0.1)

---
updated-dependencies:
- dependency-name: cryptography
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -1,5 +1,5 @@
 -i https://pypi.org/simple
-cryptography==3.4.8
+cryptography==39.0.1
 voluptuous==0.12.2
 
 alabaster==0.7.12