Fix a typo in 'Configuring Rails Applications' guide

- The initializer is called `set_autoload_paths`, not `set_autoload_path`. See https://github.com/rails/rails/blob/master/railties/lib/rails/engine.rb#L506

railties/guides/source/configuring.textile

@@ -557,7 +557,7 @@ The error occurred while evaluating nil.each
 
 *+set_load_path+* This initializer runs before +bootstrap_hook+. Adds the +vendor+, +lib+, all directories of +app+ and any paths specified by +config.load_paths+ to +$LOAD_PATH+.
 
-*+set_autoload_path+* This initializer runs before +bootstrap_hook+. Adds all sub-directories of +app+ and paths specified by +config.autoload_paths+ to +ActiveSupport::Dependencies.autoload_paths+.
+*+set_autoload_paths+* This initializer runs before +bootstrap_hook+. Adds all sub-directories of +app+ and paths specified by +config.autoload_paths+ to +ActiveSupport::Dependencies.autoload_paths+.
 
 *+add_routing_paths+* Loads (by default) all +config/routes.rb+ files (in the application and railties, including engines) and sets up the routes for the application.