Fix chapter nesting

[CI skip]
Signed-off-by: Michal Čihař <michal@cihar.com>

docs/api.rst

@@ -14,7 +14,7 @@ The API is accessible on the ``/api/`` URL and it is based on
 `Django REST framework <http://www.django-rest-framework.org/>`_.
 
 Authentication and generic parameters
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++++++++++++++++++++++++++++++++++++++
 
 The public project API is available without authentication, though
 unauthenticated requests are heavily throttled (by default to 100 requests per