Upgrade deprecated Sphinx config option in doc/

Author: neilmayhew

doc/conf.py

@@ -66,7 +66,8 @@
 
 html_theme_options = {
     'logo_only': False,
-    'display_version': False,
+    "version_selector": False,
+    "language_selector": False,
     'prev_next_buttons_location': 'bottom',
     'style_external_links': False,
     'style_nav_header_background': '#fcfcfc',