Add support for SNI and update requests.

This is the proposed fix for #534.

**WARNING: I HAVEN'T TESTED THIS.** My expectation is that it will just work, but I can't guarantee it yet. If you're happy to test locally yourself, that's great and saves me the overhead of building a NewsBlur environment. If you want me to test this, however, let me know and I'll go away and build an environment.