[w3c/manifest] dir doesn't refer to lowercase algo (#599)

There is a bug in "dir", where we write

```Otherwise, Trim(value), convert to lower-case, and let direction be the result.```

And don't refer to the lowercase algo

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/w3c/manifest/issues/599