Use the response factory instead of Guzzle for error response

[mbabker]

This package declares guzzlehttp/psr7 as a dev-only dependency, yet, the Ratchet\RFC6455\Handshake\ServerNegotiator class is directly using it in an error handling branch to create a new response. This PR replaces the incorrect use of the dev-only dependency with the response factory in this code branch.

[clue]

@mbabker Thanks for tracking this down, fix looks right to me.

This finishes off #34 which converted the other branches to the PSR-17 factory but missed this one after catching up with #23.

Could you add a test for it before we merge? That branch has no coverage today, and because the suite injects Guzzle's own HttpFactory a plain status assertion passes either way, so it has to assert the factory is actually used. This goes red on master and green with your change:

$responseFactory = $this->createMock(ResponseFactoryInterface::class);
$responseFactory->expects($this->exactly(2))
    ->method('createResponse')
    ->willReturnOnConsecutiveCalls(
        (new HttpFactory())->createResponse(),
        (new HttpFactory())->createResponse(400, 'server_max_window_bits must have a value between 8 and 15.')
    );

paired with a request carrying Sec-WebSocket-Extensions: permessage-deflate; server_max_window_bits=99.

[mbabker]

Tests updated

[clue]

@mbabker Thanks for the update, changes LGTM