update Dockerfile

[bgruening]

Seems that the latest version is not working with openjdk:8 anymore.
We got a:

Unrecognized option: --add-opens
Error: Could not create the Java Virtual Machine.

[melissalinkert]

Thanks for bringing this up, @bgruening.

As described in #239, removing support for JDK 8 was unintentional; my apologies for the inconvenience. The new 0.9.1 release should support JDK 8 again, so closing this as it should no longer be necessary. If you still see an issue with 0.9.1 though, please do let us know.

[bgruening]

Thanks for fixing it. I'm happy to close this PR. But maybe it's useful to update gradle and openjdk - which on its own is deprecated?

[sbesson]

@bgruening The Gradle version is definitely outdated as the build currently happens on Gradle 7.3.3 as defined in gradle/wrapper. As for the OpenJDK version, the library currently supports Java 8, 11 & 17 and there is currently no active plan to drop either of them.

The disconnect partly comes from the fact that none of us, certainly neither @melissalinkert nor myself, use the Dockerfile as part of our development workflow. This means the Dockerfile will go out-of-date and probably raises the wider question of whether there is still a rationale/motivation for maintaining this workflow in this repository or if it should be removed