allow phantomjs to use any encryption protocol

PhantomJS [defaults to SSLv3](http://phantomjs.org/api/command-line.html) which is vulnerable to the [POODLE attack](https://www.us-cert.gov/ncas/alerts/TA14-290A).

With SSLv3 being disabled on most servers (ours!), rendering PDF will fail with `Shrimp::RenderingError: Rendering Error: SSL handshake failed`

This allows our invocation of PhantomJS to use any available SSL protocol (TLSv1.x).