url: fix lint and deopt issues

The deopt issues arose from the use of const in specific situations
that v8 does not fully support yet.

Fixes: https://github.com/nodejs/node/issues/5299
PR-URL: https://github.com/nodejs/node/pull/5300


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>