RequireJavaVersion should use plexus-java

This rule is using SystemUtils.JAVA_VERSION to verify the Java version. The downside of this solution is that it needs to be updated every 6 month because it is using an enum to verify it.
Several other plugins already use https://codehaus-plexus.github.io/plexus-languages/plexus-java/usage.html to compare Java versions, and it doesn't require to be updated with every new Java release (as long as it keeps using the same versioning scheme of course)
Better to replace this piece of code.