Upgrade Elasticsearch CI image to v6.8.12
v6.4.2 started failing in CI due to some startup problem. Upgrade to v6.8.12 since https://hub.docker.com/_/elasticsearch says this is is a supported tag.
Edited by Stan Hu
v6.4.2 started failing in CI due to some startup problem. Upgrade to v6.8.12 since https://hub.docker.com/_/elasticsearch says this is is a supported tag.