Merge pull request #653 from searxng/dependabot/pip/master/linuxdoc-20211220

Bump linuxdoc from 20210324 to 20211220

requirements-dev.txt

@@ -13,7 +13,7 @@ sphinx-jinja==1.2.1
 sphinx-tabs==3.2.0
 sphinxcontrib-programoutput==0.17
 sphinx-autobuild==2021.3.14
-linuxdoc==20210324
+linuxdoc==20211220
 aiounittest==1.4.1
 yamllint==1.26.3
 wlc==1.12