Do not list file starting with a . in upload handler

gns3server/handlers/upload_handler.py

@@ -36,6 +36,7 @@ class UploadHandler:
         try:
             for root, _, files in os.walk(UploadHandler.image_directory()):
                 for filename in files:
+                    if not filename.startswith("."):
                         image_file = os.path.join(root, filename)
                         uploaded_files.append(image_file)
         except OSError: