Stream::__toString() must not thrown an exception

[Nyholm]

From @shaneiseminger

Method Http\Client\Socket\Stream::__toString() must not throw an exception

When using this library with happyr/linkedin-api-client, I'm getting the above fatal error. Just needs a try/catch block in __toString(). Happy to submit a pull request.

(Originally posted here: php-http/documentation#135)

[shaneiseminger]

Thanks!