Switch to use of the `release` flag rather than `source` and `target` compatibility.
Switch to use of the `release` flag rather than `source` and `target` compatibility.

This is much more robust in modern versions when targetting older versions since it configures the bootclasspath. https://stackoverflow.com/questions/43102787/what-is-the-release-flag-in-the-java-9-compiler/43103038#43103038

gocd/go-plugins,gocd/go-plugins