message: Fix typo `fresheness` -> `freshness`
diff: @@ -63,7 +63,7 @@ pub trait Source {
  /// Generates a unique string which represents the fingerprint of the
  /// current state of the source.
  ///
  - /// This fingerprint is used to determine the "fresheness" of the source
  + /// This fingerprint is used to determine the "freshness" of the source
  /// later on. It must be guaranteed that the fingerprint of a source is
  /// constant if and only if the output product will remain constant.
  ///
  