Fixed #28963 -- Raised minimum Sphinx version.

docs/conf.py

@@ -32,7 +32,7 @@ sys.path.append(abspath(join(dirname(__file__), "_ext")))
 # -- General configuration -----------------------------------------------------
 
 # If your documentation needs a minimal Sphinx version, state it here.
-needs_sphinx = '1.3'  # Actually 1.3.4, but micro versions aren't supported here.
+needs_sphinx = '1.5.5'
 
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.