use deamon threads in the ProcessExecutor

src/de/uni_passau/fim/seibt/gitwrapper/process/ProcessExecutor.java

@@ -25,7 +25,13 @@ import static java.util.logging.Level.WARNING;
 public class ProcessExecutor {
 
     private static final Logger LOG = Logger.getLogger(ProcessExecutor.class.getCanonicalName());
-    private static final ExecutorService exService = Executors.newCachedThreadPool();
+
+    private static final ExecutorService exService = Executors.newCachedThreadPool(r -> {
+        Thread t = Executors.defaultThreadFactory().newThread(r);
+
+        t.setDaemon(true);
+        return t;
+    });
 
     /**
      * The result of a process execution.