Bump future from 0.18.2 to 0.18.3 in /doc

Bumps [future](https://github.com/PythonCharmers/python-future) from 0.18.2 to 0.18.3.
- [Release notes](https://github.com/PythonCharmers/python-future/releases)
- [Changelog](https://github.com/PythonCharmers/python-future/blob/master/docs/changelog.rst)
- [Commits](PythonCharmers/python-future@v0.18.2...v0.18.3)

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

Signed-off-by: dependabot[bot] <[email protected]>

doc/requirements.txt

@@ -7,7 +7,7 @@ cachetools==5.0.0
 certifi==2023.7.22
 charset-normalizer==2.0.12
 docutils==0.16
-future==0.18.2
+future==0.18.3
 idna==3.3
 imagesize==1.3.0
 importlib-metadata==4.11.3