Fix to make the code work with Sphinx 1.6.1

See sphinx-contrib#39

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')