flags: fix wording in comment for LetsEncryptCache
flags: fix wording in comment for LetsEncryptCache

Add a missing word and s/user/owner/ for clarity

Change-Id: I1ba83bcb413695f5dc354c9d0522a56bb6c47585
Reviewed-on: https://upspin-review.googlesource.com/7813
Reviewed-by: Bons <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@google.com>

upspin/upspin,upspin/upspin