Use the protocol version sent by the client

Use the protocol version sent by the client. This should be the latest version supported by the client, which may also be the only acceptable. This makes this module work with SSLv3, TLSv1.0, TLSv1.1, and TLSv1.2 when NEGOTIATE_TLS is not enabled (see https://gist.github.com/rcvalle/10335282).