Squirrel version(s)
2.0.1

Description
RestartApp causing AbandonedMutexException

Steps to recreate

1. Start up application that is using GitHubUpdateManager
2. Leave the application running for 5 minutes (to ensure app has finished update process)
3. Select manual user action that calls to UpdateManager.RestartApp();

Expected behavior
The application should restart without causing an exception

Actual behavior
The application does restart but an exception is logged in event log:
"Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.Threading.AbandonedMutexException
at Squirrel.SingleGlobalInstance.Finalize()"

This occurs as old version is shutting down.

Additional information
I have a c# winform application with the following code in program.cs:
` static async Task Main()
//static void Main()
{
AppLogging.WriteLog("Checking for updates...");

        using (var mgr = UpdateManager.GitHubUpdateManager(Properties.Settings.Default.GitHubPath))
          // "https://github.com/grips-tiresoft/webprintingapp"
        {
            try
            {
                await  mgr.Result.UpdateApp();
                mgr.Result.CreateRunAtWindowsStartupRegistry();
            }
            catch (Exception e)
            {
                AppLogging.WriteLog(string.Format("Exception: {0} occurred, message: {1}", e.InnerException.GetType().ToString(), e.InnerException.Message));
            }
        }

        AppLogging.WriteLog("Update Check completed");

There is action that user can invoke:

private void Restart_Click(object sender, EventArgs e) { UpdateManager.RestartApp(); }

Additionally, no message was logged in catch statement above, so it is not occurring during the update phase.