Put return type of __len__ in correct column (#2975)

docs/src/userguide/special_methods.rst

@@ -375,7 +375,7 @@ https://docs.python.org/3/reference/datamodel.html#emulating-container-types
 +-----------------------+---------------------------------------+-------------+-----------------------------------------------------+
 | Name 	                | Parameters                            | Return type | 	Description                                 |
 +=======================+=======================================+=============+=====================================================+
-| __len__ 	        | self 	int 	                        |             | len(self)                                           |
+| __len__               | self                                  | int         | len(self)                                           |
 +-----------------------+---------------------------------------+-------------+-----------------------------------------------------+
 | __getitem__ 	        | self, x 	                        | object      | self[x]                                             |
 +-----------------------+---------------------------------------+-------------+-----------------------------------------------------+