Log Message:
databases/elasticsearch: Update to 6.4.0.

6.4.0 release highlights

Analysis
- Option to index phrases on text fields
- Korean analysis tools
- Add multiplexing token filter

Machine learning
- Improve your machine learning results with custom rules
- The {ml} analytics can now detect specific change points in a time
  series

Mappings
- alias field type
- _ignored meta field

Rank Eval API
- Expected Reciprocal Rank metric for Rank Eval API

Search
- Cross Cluster Search will no longer use dedicated master nodes as
  gateway nodes
- Format option for doc_value fields
- Support second level of field collapse

Security
- Kerberos authentication support is now available
- {es} now offers a FIPS 140-2 compliant mode

6.3.0 release highlights

- SQL: This experimental feature enables users who are familiar with
  SQL to use SQL statements to query {es} indices.
- Rollups: This experimental feature enables you to summarize and
  store historical data so that is still available for analysis, but
  consumes significantly less storage space.
- Java 10 Support

For full releases since 6.2.4 please see

https://www.elastic.co/guide/en/elasticsearch/reference/6.4/release-notes-6.3.1.html
https://www.elastic.co/guide/en/elasticsearch/reference/6.4/release-notes-6.3.2.html
https://www.elastic.co/guide/en/elasticsearch/reference/6.4/release-notes-6.3.0.html
https://www.elastic.co/guide/en/elasticsearch/reference/6.4/release-notes-6.4.0.html