Missing documentation for error response from screenshot API

[scottgonzalez]

When requesting a screenshot with the JSON format, errors are reported differently than documented in the Error Handling section. There is no mention of how to handle errors in this case. From my experience, you just get back an object with an error property containing the error message.

[scottgonzalez]

The error reporting has been fixed, as noted in scottgonzalez/node-browserstack#18 (comment).