message: fix delete error msg
diff: @@ -198,7 +198,7 @@ impl fmt::Display for DeleteError {
  }
  DeleteError::IOError(ref err) => {
  write!(f,
  - "an io error occurred while opening a file for reading: '{}'",
  + "an io error occurred while deleting a file: '{}'",
  err)
  }
  }
  @@ -207,7 +207,7 @@ impl fmt::Display for DeleteError {
  impl StdError for DeleteError {
  fn description(&self) -> &str {
  - "error occurred while opening a file for reading"
  + "error occurred while deleting a file"
  }
  fn cause(&self) -> Option<&StdError> {
  