doc: fix improper http.get sample code

Refs: https://github.com/nodejs/node-v0.x-archive/pull/25471
Refs: https://github.com/nodejs/node-v0.x-archive/issues/8443
PR-URL: https://github.com/nodejs/node/pull/4263


Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>