Use --release flag for correct cross-compilation

[pascalgn]

When using this plugin with Java 8 and setting -Dexists.cmpChecksum=true, the Maven process exists with the error

Caused by: org.apache.maven.plugin.PluginContainerException: An API incompatibility was encountered while executing org.honton.chas:exists-maven-plugin:0.1.0:remote: java.lang.NoSuchMethodError: java.nio.ByteBuffer.flip()Ljava/nio/ByteBuffer;
[...]
Caused by: java.lang.NoSuchMethodError: java.nio.ByteBuffer.flip()Ljava/nio/ByteBuffer;
    at org.honton.chas.exists.CheckSum.readStream (CheckSum.java:48)
    at org.honton.chas.exists.CheckSum.getChecksumBytes (CheckSum.java:30)
    at org.honton.chas.exists.CheckSum.getChecksum (CheckSum.java:37)

The cause is the same as in e.g. plasma-umass/doppio#497

The fix is to use the --release flag, as explained in e.g. https://stackoverflow.com/questions/43102787/what-is-the-release-flag-in-the-java-9-compiler

As --release is only available from Java 9 on, I had to put the property in a profile

[chonton]

Looks good. I have another regression to fix before next release.

[pascalgn]

@chonton Any plans to release this soon? 🙏

[chonton]

Yes, this was released in mid January. My apologies for not tagging this repository

[pascalgn]

Ah, perfect! Thanks a lot, everything works fine now! 👍