Fix the builder

Author: nakamura-to

.readthedocs.yaml

@@ -14,7 +14,7 @@ build:
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/conf.py
-  builder: "dirhtml"
+  builder: dirhtml
 
 # We recommend specifying your dependencies to enable reproducible builds:
 # https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html