Fix example: Pipeline needs to return the Ajax object

https://datatables.net/forums/discussion/60074/reference-to-xhr-not-passed-for-xhr-dt-when-using-pipline-plugin#latest

examples/server_side/pipeline.xml

@@ -85,7 +85,7 @@ $.fn.dataTable.pipeline = function ( opts ) {
 				$.extend( request, conf.data );
 			}
 
-			settings.jqXHR = $.ajax( {
+			return $.ajax( {
 				"type":     conf.method,
 				"url":      conf.url,
 				"data":     request,