Clear response when re-invoking a method on the hub

[ramiabughazaleh]

Hi.

When invoking a long running method on a SignalR hub, and the method was previously invoked, values currently in the response box are not cleared.

Since there is no indication of activity after invoking a method, it makes it harder to tell if the current values in the response box are from the previous invocation, and the current invocation is still running, or if the method has already finished.

Thank you.