Bump linuxdoc from 20210110 to 20210324

Bumps [linuxdoc](https://github.com/return42/linuxdoc) from 20210110 to 20210324.
- [Release notes](https://github.com/return42/linuxdoc/releases)
- [Commits](https://github.com/return42/linuxdoc/commits)

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

requirements-dev.txt

@@ -14,4 +14,4 @@ sphinx-jinja==1.1.1
 sphinx-tabs==2.1.0
 sphinxcontrib-programoutput==0.16
 sphinx-autobuild==2020.9.1
-linuxdoc==20210110
+linuxdoc==20210324