Update WebSocketManagerExtensions.cs
Update WebSocketManagerExtensions.cs

for the situation if my subclass inherits from WebSocketHandler does not exist in the entry assembly.
so I can setup in the startup.cs like this:
`services.AddWebSocketManager(Assembly.GetAssembly(typeof(NotifierHub)));`
radu-matei/websocket-manager,radu-matei/websocket-manager,radu-matei/websocket-manager