Don't check blacklist if SSL verification is off

It's helpful to be able to test the bindings with instances of the
Stripe API running locally, or running on a server that doesn't support
SSL. When :verify_ssl_certs is false, don't check the SSL cert against
the blacklist, as there probably isn't a certificate to check.
Merge pull request #139 from stripe/truly_disable_ssl

Don't check blacklist if SSL verification is off