revert rtd config

.readthedocs.yml

@@ -10,7 +10,7 @@ sphinx:
   configuration: docs/source/conf.py
   # fail_on_warning might generate hard to fix error, in this case it can be
   # disabled but this also means those errors will fail silently, choose wisely.
-  # fail_on_warning: true
+  fail_on_warning: true
 
 # Build documentation with MkDocs
 #mkdocs: