textproc/elasticsearch6: Update to 6.8.12

Changes: https://www.elastic.co/guide/en/elasticsearch/reference/6.8/release-notes-6.8.12.html
PR: 248761
Submitted by: Juraj Lutter <juraj@lutter.sk> (maintainer)
MFH: 2020Q3
Security: fbca6863-e2ad-11ea-9d39-00a09858faf5