Alias expansion in "to" field needed

[rvagg]

See #56.

I don't think that mailgun supports recursive aliases. So you can do ctc@ -> tsc@, you have to double-up the list. So what we should do with the update app in this repo is adjust it so that if any aliases are recognised in the "to" list (i.e. any [email protected] in the iojs.org aliases list) get expanded to what's in that list itself. So we can then use recursive aliases locally in aliases.json but mailgun only sees the full lists.