Correct the return code description for 204

doc/api/README.md

@@ -159,7 +159,7 @@ The following table shows the possible return codes for API requests.
 | Return values | Description |
 | ------------- | ----------- |
 | `200 OK` | The `GET`, `PUT` or `DELETE` request was successful, the resource(s) itself is returned as JSON. |
-| `204 OK` | The server has successfully fulfilled the request and that there is no additional content to send in the response payload body. |
+| `204 No Content` | The server has successfully fulfilled the request and that there is no additional content to send in the response payload body. |
 | `201 Created` | The `POST` request was successful and the resource is returned as JSON. |
 | `304 Not Modified` | Indicates that the resource has not been modified since the last request. |
 | `400 Bad Request` | A required attribute of the API request is missing, e.g., the title of an issue is not given. |