shutdown executor service for the parallel update scheme in the post loop method.

VadereSimulator/src/org/vadere/simulator/models/osm/OptimalStepsModel.java

@@ -279,6 +279,7 @@ public class OptimalStepsModel implements MainModel, PotentialFieldModel {
 
 	@Override
 	public void postLoop(final double simTimeInSec) {
+		updateSchemeOSM.shutdown();
 	}
 
 	@Override

VadereSimulator/src/org/vadere/simulator/models/osm/updateScheme/UpdateSchemeOSM.java

@@ -117,4 +117,8 @@ public interface UpdateSchemeOSM extends DynamicElementRemoveListener<Pedestrian
 			topography.moveElement(pedestrian, from);
 		}
 	}
+
+	default void shutdown() {
+
+	}
 }

VadereSimulator/src/org/vadere/simulator/models/osm/updateScheme/UpdateSchemeParallel.java

@@ -230,4 +230,9 @@ public class UpdateSchemeParallel implements UpdateSchemeOSM {
 
 	@Override
 	public void elementRemoved(Pedestrian element) {}
+
+	@Override
+	public void shutdown() {
+		executorService.shutdown();
+	}
 }