A minor change to hopefully reduce inane warnings from visual studio.

examples/dnn_face_recognition_ex.cpp

@@ -19,10 +19,10 @@
     dnn_metric_learning_on_images_ex.cpp examples.
 */
 
+#include <dlib/dnn.h>
 #include <dlib/gui_widgets.h>
 #include <dlib/clustering.h>
 #include <dlib/string.h>
-#include <dlib/dnn.h>
 #include <dlib/image_io.h>
 #include <dlib/image_processing/frontal_face_detector.h>