video_name in dumped file for interpolation mode (#446)

* Add video source in dumped file for interpolation mode.
* remove trailing whitespace

cvat/apps/engine/annotation.py

@@ -1293,6 +1293,8 @@ class TaskAnnotation:
                 ("width", str(im_meta_data[0]["width"])),
                 ("height", str(im_meta_data[0]["height"]))
             ])
+            # Add source to dumped file
+            meta["source"] = str(db_task.video.path)
 
         with open(file_path, "w") as dump_file:
             dumper = XmlAnnotationWriter(dump_file)