Rebuild image regularly to pull in security fixes from node

[albuch]

To get all Node and Alpine security fixes in more frequently an automated build could be set up in Docker Hub listening on upstream repository changes via Repository links.
https://docs.docker.com/docker-hub/builds/#repository-links

If corresponding node image changes the vault-ui image could be rebuilt and re-published under the same tag.

Currently vault-ui 2.2.0 image has these security issues:

[djenriquez]

@albuch, a repository link to node was added:

Thanks for the suggestion!

[albuch]

Awesome, thanks @djenriquez