Bump elasticsearch from 6.3.1 to 6.4.0 (#5918)
Bump elasticsearch from 6.3.1 to 6.4.0 (#5918)

Bumps [elasticsearch](https://github.com/elastic/elasticsearch-py) from 6.3.1 to 6.4.0.
- [Release notes](https://github.com/elastic/elasticsearch-py/releases)
- [Changelog](https://github.com/elastic/elasticsearch-py/blob/6.4.0/Changelog.rst)
- [Commits](https://github.com/elastic/elasticsearch-py/compare/6.3.1...6.4.0)
pypa/warehouse,pypa/warehouse,pypa/warehouse,pypa/warehouse