base64url-encode condition in header

[michielbdejong]

Discovered this issue while reviewing #34, must be a left-over from a merge conflict we had last month.

[michielbdejong]

The condition obviously needs to be base64url-encoded, otherwise you get this error:

TypeError: The header content contains invalid characters
at ServerResponse.setHeader (_http_outgoing.js:374:11)
at Server. (/Users/michiel/gh/interledger/tutorials/letter-shop/completed/shop.js:78:11)
at emitTwo (events.js:106:13)
at Server.emit (events.js:194:7)
at parserOnIncoming (_http_server.js:565:12)
at HTTPParser.parserOnHeadersComplete (_http_common.js:99:23)

[michielbdejong]

Deprecated.