Update databases/elasticsearch to 5.6.3.

=== Enhancements

Network::
* Add additional low-level logging handler
* Unwrap exception causes when checking if  dying

=== Bug fixes

Aggregations::
* Fix IndexOutOfBoundsException in histograms for NaN doubles

Core::
* MetaData Builder doesn't properly prevent an alias with the same
* name as an index

Packaging::
* Fix default paths for Windows service

Plugin Repository Azure::
* Use Azure upload method instead of our own implementation

Search::
* Fix serialization errors when cross cluster search goes to a single
* shard

(fhajny)