Doc fix: bulk_index -> bulk rename

Author: honzakral

elasticsearch/client/__init__.py

@@ -508,8 +508,8 @@ def bulk(self, body, index=None, doc_type=None, params=None):
  Perform many index/delete operations in a single API call.
  `<http://elasticsearch.org/guide/reference/api/bulk/>`_
 
- See the :func:`~elasticsearch.helpers.bulk_index` for a more friendly
- API.
+ See the :func:`~elasticsearch.helpers.bulk` helper function for a more
+ friendly API.
 
  :arg body: The operation definition and data (action-data pairs), as
  either a newline separated string, or a sequence of dicts to