fix #494 -- close DocumentPage to free up open connections

(cherry picked from commit 7f89112)

Author: sammefford

src/main/java/com/marklogic/client/datamovement/ExportListener.java

@@ -101,8 +101,7 @@ protected DocumentPage getDocs(QueryBatch batch) {
    */
   @Override
   public void processEvent(QueryBatch batch) {
-    try {
-      DocumentPage docs = getDocs(batch);
+    try ( DocumentPage docs = getDocs(batch) ) {
       while ( docs.hasNext() ) {
         for ( Consumer<DocumentRecord> listener : exportListeners ) {
           try {