Fixed type conversion issue with isProtocol method in HyBi10.php

I encountered the following error while attempting to use Ratchet. The __toString version of the request should contain the proper value, and retrieving the string before converting to an int would prevent this typecasting issue.

Notice: Object of class Guzzle\Http\Message\Header could not be converted to int in [file system path]\vendor\cboden\ratchet\src\Ratchet\WebSocket\Version\HyBi10.php on line 7