chore(deps): Update dependency sphinxcontrib.serializinghtml to v2

Author: renovate[bot]

requirements.txt

@@ -6,5 +6,5 @@ sphinxcontrib-applehelp==1.0.4
 sphinxcontrib.devhelp==1.0.2
 sphinxcontrib.htmlhelp==2.0.0
 sphinxcontrib.qthelp==1.0.3
-sphinxcontrib.serializinghtml==1.1.5
+sphinxcontrib.serializinghtml==2.0.0
 standard-imghdr==3.13.0