Fix Web Integration Service library api example by using the webserver_option() function instead of the old document_root() function

Author: fgallegosalido

examples/web_integration_service/library_api/c++11/web_integration_service_library_api.cxx

@@ -36,8 +36,10 @@ void service_main(
 {
     rti::webdds::ServiceProperty service_property;
 
-    service_property.cfgfile(cfg_file).cfgname(cfg_name).document_root(
-            document_root);
+    service_property
+            .cfgfile(cfg_file)
+            .cfgname(cfg_name)
+            .webserver_option("document_root", document_root);
 
     rti::webdds::Service service(std::move(service_property));