1.6 compat:dereference deprecated default_sidebars

StandaloneHTMLBuilder.default_sidebars was removed in sphinx ~1.6.

sphinx-doc/sphinx@e8e63b1#diff-c17608ed63bfe1714c6befb9d4201fee

Author: Lingnik

sphinxcontrib/versioning/sphinx_.py

@@ -57,7 +57,7 @@ def builder_inited(app):
 
         # Add versions.html to sidebar.
         if '**' not in app.config.html_sidebars:
-            app.config.html_sidebars['**'] = StandaloneHTMLBuilder.default_sidebars + ['versions.html']
+            app.config.html_sidebars['**'] = ['versions.html']
         elif 'versions.html' not in app.config.html_sidebars['**']:
             app.config.html_sidebars['**'].append('versions.html')