launch: add CORS headers to /who endpoint
Necessary to allow bridge to make a cross-origin request via
javascript.
[[%404 ~] ~]
=/ response=json
(frond:enjs:format %who (ship:enjs:format p.bek))
-(json-response:gen (json-to-octs response))
+:-
+ :- %200
+ :~
+ ['content-type' 'application/json']
+ ['access-control-allow-origin' 'https://bridge.urbit.org']
+ ==
+`(json-to-octs response)
