Invalid JSON in the Service Builder section

Thanks for a great library!

I was working through the [Service Builder](http://guzzlephp.org/webservice-client/webservice-client.html#service-builder) section, and the JSON in the example is invalid. I verified by copy-and-pasting the example into http://jsonlint.com/ which confirmed that the backslashes in the class name need to be escaped.

Thanks,
Chris