Fix missing close curly bracket

[Lai-YT]

It seems like we're missing a close curly bracket (}), which encloses the body of the Tail recursive sum function.

const sum = list => {
  const go = (acc, xs) =>
    xs.length === 0
      ? acc
      : go(acc + first(xs), rest(xs));
  return go(0, list) 
}  // <- this one is missing

English ver. and Korean ver. are both fixed 😄 Thank you for making such great repo 🚀