Mark FileSystemTree thread as daemon

Otherwise, the JVM cannot shut down cleanly.

Author: ctrueden

src/main/java/org/scijava/ui/swing/script/FileSystemTree.java

@@ -506,6 +506,7 @@ private class DirectoryWatcher extends Thread {
 		private final HashMap<Path, Node> map = new HashMap<>();
 
 		DirectoryWatcher() {
+			setDaemon(true);
 			try {
 				this.watcher = FileSystems.getDefault().newWatchService();
 				this.start();