conf.py: Fix syntax error in sphinx_rtd_theme option

conf.py

@@ -56,7 +56,7 @@ if not on_rtd:  # only import and set the theme if we're building docs locally
 
 # Theme options
 html_theme_options = {
-  "collapse_navigation": "True",
+  "collapse_navigation": True,
 }
 
 # Output file base name for HTML help builder