Update docs/source/api.rst

Co-authored-by: Adrián Chaves <[email protected]>

Author: radostyle

docs/source/api.rst

@@ -518,7 +518,7 @@ Encoding that's used to encode log messages.
 Default: ``utf-8``.
 
 DEFAULT_ERRBACK_NAME
-~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~
 
 The name of the default errback method to call on the spider in case of an exception. The default errback method is ``parse`` to maintain backwards compatibility but it is not standard to scrapy and may interfere with the use of middlewares which implement the ``process_spider_exception`` method. Use a setting of ``None`` if you don't want to use the default scrapy exception handling.