Currently, icons will fail to load if the player is placed inside an iframe without a window.location. This adds an additional check to use `window.top.location` if the window does not have a location.
* Fix to work inside iframes.
Right now Plyr fails to load inside iframes because the selectors are not instances of Element (iframes have their own, separate globals). This is an alternative method to check isElement that will work inside iframes. This is battle-tested fallback code used before browsers supported HTMLElement.
* Update is.js