Update README to reflect default WARNING color

Author: tiliv

README.md

@@ -47,7 +47,7 @@ By subclassing the formatter, you can override the custom `configure_style()` me
     def configure_style(self, style):
         style.DEBUG = style.HTTP_NOT_MODIFIED
         style.INFO = style.HTTP_INFO
-        style.WARNING = style.HTTP_REDIRECT
+        style.WARNING = style.HTTP_NOT_FOUND
         style.ERROR = style.ERROR
         style.CRITICAL = style.HTTP_SERVER_ERROR
         return style