Fix issue with promises
During the development of plugins we faced a problem with exceptions thrown in plugins.
Any exceptions not implementing Http\Client\Exception
ended up in an invalid argument error because of these lines:
https://github.com/php-http/promise/blob/v1.0.0/src/RejectedPromise.php#L36-L38
This type leak allowed to inject an exception to be passed to the onRejected callback of a Promise.
In the current release we introduced HTTP specific promises which does not catch all exceptions, but HTTP ones. Every other exception will be thrown immediately.