Use SIGUSR1 to softstop

src/de/steamwar/bungeecore/Subserver.java

@@ -136,10 +136,15 @@ public class Subserver {
     }
 
     public void stop() {
-        if(checkpoint)
-            process.children().forEach(ProcessHandle::destroy);
-        else
-            execute("stop");
+        try {
+            long pid = process.pid();
+            if(checkpoint)
+                pid = process.children().findAny().map(ProcessHandle::pid).orElse(pid);
+
+            Runtime.getRuntime().exec(new String[]{"kill", "-SIGUSR1", Long.toString(pid)});
+        } catch (IOException e) {
+            ProxyServer.getInstance().getLogger().log(Level.SEVERE, "Failed to send SIGUSR1 to subserver.", e);
+        }
 
         try {
             if(!process.waitFor(1, TimeUnit.MINUTES))