That damn Nitro popup

When I launch Discord I get a popup ad. I'm not interested in it, but there's no X to make it go away. I quit and relaunched Discord, but the same damn ad shows up again. 

I found another post about a popup that won't close. How silly of me not to know that Command-R would make it go away … and reappear. 

Make it stop! I do not want this! Olay, okay, FINE. I'll click the Read More … and then close it. Don't get in the way of me using the app.