Mixpanel's track() does not fire callback

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I'm not sure what happens but sometimes track() does not fire callback. For now, I add a workaround snippet to fire callbacks, but It's better if mixpanel-js handles it.

My workaround is something like that:

    const timeoutId = setTimeout(() => {
      window.location.assign(newPath);
    }, 5000 /* timeout */);

    mkxpanel.track(a, b, () => {
      clearTimeout(timeoutId);
      window.location.assign(newPath);
    });

I think XMLHttpRequest#timeout should be set, anyway.