Support for Java 16

[therockstorm]

Are you open to adding support for Java 16 to the build matrix? The baseImageTag would be 16-jdk-buster.

[francisdb]

My idea was supporting lts + latest and greatest. We would then replace 15 with 16. On the other hand maybe we could stick to all the versions that still get support. I wonder if docker hub has some kind of limit in the number of images we can publish.

[francisdb]

Will see if anybody complains about jdk15 builds no longer getting new images

[francisdb]

images pushed and available here:
https://hub.docker.com/r/hseeberger/scala-sbt/tags?page=1&ordering=last_updated&name=16_

[therockstorm]

Thanks!