message: Fix spine pretty printing
diff: @@ -369,6 +369,7 @@ impl ToDoc for Value {
  Doc::text(";").append(Doc::space()),
  ))
  .append("]"),
  + Value::Neutral(ref neutral, ref spine) if spine.is_empty() => neutral.to_doc(),
  Value::Neutral(ref neutral, ref spine) => {
  pretty_app(neutral.to_doc(), spine.iter().map(|arg| &arg.inner))
  },
  