The `url` module is not a constructor; change `require('url')` to
`require('url').URL`. Also, check the entire origin rather than just
the hostname, since otherwise `http://my-own-server.com` is allowed in
addition to `https://my-own-server.com`, in violation of point 1 (only
load secure content).
Signed-off-by: Anders Kaseorg <andersk@mit.edu>