message: remove deprecated Error::cause
diff: @@ -67,12 +67,7 @@ pub enum Error {
  ExportError(quick_xml::Error),
  }
  -impl error::Error for Error {
  - #[inline]
  - fn cause(&self) -> Option<&dyn error::Error> {
  - None
  - }
  -}
  +impl error::Error for Error {}
  impl fmt::Display for Error {
  #[inline]
  