message: Provide single quote separators around missing Cargo.toml field to improve readability
diff: @@ -156,7 +156,7 @@ pub fn write_package_json(
  let warn_fmt = |field| {
  format!(
  - "Field {} is missing from Cargo.toml. It is not necessary, but recommended",
  + "Field '{}' is missing from Cargo.toml. It is not necessary, but recommended",
  field
  )
  };
  