Enable MkDocs strict mode again

Author: marcelstoer

mkdocs.yml

@@ -2,8 +2,9 @@ site_name: NodeMCU Documentation
 site_description: Description of the NodeMCU documentation
 repo_url: https://github.com/nodemcu/nodemcu-firmware/
 
-theme: readthedocs
-strict: false # mustn't be true due to https://github.com/rtfd/readthedocs.org/issues/4314 
+theme:
+  name: "readthedocs"
+strict: true
 
 markdown_extensions:
 #http://pythonhosted.org/Markdown/extensions/admonition.html