message: remove derivation of Copy when we have instance of Drop
diff: @@ -124,7 +124,7 @@ pub type Result<T> = result::Result<T, Error>;
  ///
  /// See module documentation for mode details about how to use
  /// `Entropy`.
  -#[derive(PartialEq, Eq, PartialOrd, Ord, Copy, Clone)]
  +#[derive(PartialEq, Eq, PartialOrd, Ord, Clone)]
  pub enum Entropy {
  Entropy12([u8;16]),
  Entropy15([u8;20]),
  