Use proper retry_on_conflict for helpers.expand_action

As per https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-bulk.html#bulk-update, retry_on_conflict should not be preceeded by an underscore.

Author: msukmanowsky

elasticsearch/helpers/__init__.py

@@ -38,7 +38,7 @@ def expand_action(data):
  action = {op_type: {}}
  for key in ('_index', '_parent', '_percolate', '_routing', '_timestamp',
  '_type', '_version', '_version_type', '_id',
- '_retry_on_conflict', 'pipeline'):
+ 'retry_on_conflict', 'pipeline'):
  if key in data:
  action[op_type][key] = data.pop(key)