build(deps): bump sphinxcontrib-devhelp from 1.0.5 to 1.0.6 in /docs

Bumps [sphinxcontrib-devhelp](https://github.com/sphinx-doc/sphinxcontrib-devhelp) from 1.0.5 to 1.0.6.
- [Release notes](https://github.com/sphinx-doc/sphinxcontrib-devhelp/releases)
- [Changelog](https://github.com/sphinx-doc/sphinxcontrib-devhelp/blob/1.0.6/CHANGES)
- [Commits](sphinx-doc/sphinxcontrib-devhelp@1.0.5...1.0.6)

---
updated-dependencies:
- dependency-name: sphinxcontrib-devhelp
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

docs/requirements.txt

@@ -19,7 +19,7 @@ snowballstemmer==2.2.0
 sphinx-favicon==1.0.1
 sphinx-rtd-theme==2.0.0
 sphinxcontrib-applehelp==1.0.8
-sphinxcontrib-devhelp==1.0.5
+sphinxcontrib-devhelp==1.0.6
 sphinxcontrib-htmlhelp==2.0.5
 sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-qthelp==1.0.6