fix: Exception on server disconnect -> ServerDisconnect is not raised

[mortarroad]

I get the following exception when stopping the server (Intiface Central 3.1.0 via the Stop button) while connected:

System.InvalidOperationException: A task may only be disposed if it is in a completion state (RanToCompletion, Faulted or Canceled).
  at System.Threading.Tasks.Task.Dispose (System.Boolean disposing)
  at System.Threading.Tasks.Task.Dispose ()
  at Buttplug.Client.ButtplugWebsocketConnector.RunClientLoop (System.Threading.CancellationToken token) in Buttplug/Client/ButtplugWebsocketConnector.cs:135

This results in the ButtplugClient.ServerDisconnect event not being raised.

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I think the Dispose was meant to set the task to "fire-and-forget". That can be achieved by just discarding the return value.

According to https://devblogs.microsoft.com/dotnet/do-i-need-to-dispose-of-tasks/, tasks do not need to be disposed anyway.

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