message: use path when serializing a package
diff: @@ -63,7 +63,7 @@ struct SerializedPackage<'a> {
  dependencies: &'a [Dependency],
  targets: Vec<&'a Target>,
  features: &'a FeatureMap,
  - manifest_path: &'a str,
  + manifest_path: &'a Path,
  metadata: Option<&'a toml::Value>,
  authors: &'a [String],
  categories: &'a [String],
  @@ -113,7 +113,7 @@ impl ser::Serialize for Package {
  dependencies: summary.dependencies(),
  targets,
  features: summary.features(),
  - manifest_path: &self.manifest_path.display().to_string(),
  + manifest_path: &self.manifest_path,
  metadata: self.manifest.custom_metadata(),
  authors,
  categories,
  