build(deps): bump sphinx from 3.5.4 to 4.0.1 in /docs

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.5.4 to 4.0.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/4.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.5.4...v4.0.1)

Signed-off-by: dependabot[bot] <support@github.com>
Signed-off-by: Ryan Northey <ryan@synca.io>

docs/requirements.txt

@@ -161,9 +161,9 @@ sphinx-tabs==3.0.0 \
     --hash=sha256:2abbcaaa3b8a857de06f3db31762a7bdd17aba1b8979d000f193debe6f917c2c \
     --hash=sha256:3f766762fffacc99828cb877a9e4cb8ac0ba3582f2a054ea68248e5e026e5612
     # via -r docs/requirements.txt
-sphinx==3.5.4 \
-    --hash=sha256:19010b7b9fa0dc7756a6e105b2aacd3a80f798af3c25c273be64d7beeb482cb1 \
-    --hash=sha256:2320d4e994a191f4b4be27da514e46b3d6b420f2ff895d064f52415d342461e8
+sphinx==4.0.1 \
+    --hash=sha256:b2566f5f339737a6ef37198c47d56de1f4a746c722bebdb2fe045c34bfd8b9d0 \
+    --hash=sha256:cf5104777571b2b7f06fa88ee08fade24563f4a0594cf4bd17d31c47b8740b4c
     # via
     #   -r docs/requirements.txt
     #   sphinx-copybutton