make db-updater daemon thread

src/main/java/com/sparrowwallet/sparrow/io/db/DbPersistence.java

@@ -166,7 +166,7 @@ public class DbPersistence implements Persistence {
 
     private synchronized void createUpdateExecutor(Wallet masterWallet) {
         if(updateExecutor == null) {
-            BasicThreadFactory factory = new BasicThreadFactory.Builder().namingPattern(masterWallet.getFullName() + "-dbupdater").daemon(false).priority(Thread.NORM_PRIORITY).build();
+            BasicThreadFactory factory = new BasicThreadFactory.Builder().namingPattern(masterWallet.getFullName() + "-dbupdater").daemon(true).priority(Thread.NORM_PRIORITY).build();
             updateExecutor = Executors.newSingleThreadExecutor(factory);
         }
     }