Stops jettyServer before destroying it

Change-Id: I34e3d076fdff654d0cf021dac90f5ef15d276098
diff --git a/src/main/java/de/ids_mannheim/korap/plkexport/PluginServer.java b/src/main/java/de/ids_mannheim/korap/plkexport/PluginServer.java
index ca0c4c9..8a6421d 100644
--- a/src/main/java/de/ids_mannheim/korap/plkexport/PluginServer.java
+++ b/src/main/java/de/ids_mannheim/korap/plkexport/PluginServer.java
@@ -73,6 +73,7 @@
             jettyServer.join();
         }
         finally {
+            jettyServer.stop();
             jettyServer.destroy();
         }
     }