Add Release flag/configuration to Maven Compiler Plugin #20

When compiling the project with more recent JDKs (9+) there is the possibility of using more recent Java features in new code (while still targeting Java 8 with the library). An example would be List.getLast(). It will compile but only fail when used in a Java 8 runtime ... The release configuration/flag ensures that the project is compiled with features only available in the expected JDK version. (Java 8 for cql-java.)

See here for more details: https://maven.apache.org/plugins/maven-compiler-plugin/examples/set-compiler-release.html
This however requires a more recent version (3.6+) of maven-compiler-plugin. Which might not work in JDK 8 runtimes? (I'm not sure about this. And documentation is a bit scarce...)