elasticsearch:6.1 docker image not available any more

README.md shows a user to run elasticsearch:6.1, but this does not work now.

docker run -itd -p 9200:9200 elasticsearch:6.1

Tests

6.1

$ docker pull elasticsearch:6.1
Error response from daemon: manifest for elasticsearch:6.1 not found: manifest unknown: manifest unknown

6.8.6

6.8.6 is the latest version of 6.x (6.8.7 is not released yet) according to https://www.elastic.co/guide/en/elasticsearch/reference/6.8/es-release-notes.html:

$ docker pull elasticsearch:6.8.6
6.8.6: Pulling from library/elasticsearch
ab5ef0e58194: Pulling fs layer 
[...]

cf. https://hub.docker.com/_/elasticsearch?tab=tags&page=1&name=6.1