Copy calculated JAVA_HOME path to make sure maven works

Sometimes rascal is running inside of a jdk that is not the same as JAVA_HOME, or JAVA_HOME is note defined

Fixes #1770

src/org/rascalmpl/library/util/PathConfig.java

@@ -664,6 +664,7 @@ private static IList getPomXmlCompilerClasspath(ISourceLocation manifestRoot) {
             ProcessBuilder processBuilder = new ProcessBuilder(mvnCommand, "--batch-mode", "-o", "dependency:build-classpath",
                 "-DincludeScope=compile");
             processBuilder.directory(new File(manifestRoot.getPath()));
+            processBuilder.environment().put("JAVA_HOME", System.getProperty("java.home", System.getenv("JAVA_HOME")));
 
             Process process = processBuilder.start();