Event handler called multiple times if path are same.

[mark-liner]

First of all, thank you for your great module. I couldn't have finished my project without it.

When creating ads on infinite scroll screen, I had to use same ad units in Google Ad Manager.

  if (onSlotRenderEnded) {
    googletag.cmd.push(() => {
      googletag.pubads().addEventListener('slotRenderEnded', (event) => {
        // check if the current slot is the one the callback was added to
        // (as addEventListener is global)
        if (event.slot.getAdUnitPath() === path) {
          onSlotRenderEnded(event);
        }
      });
    });
  }

Above code only check the path of the ad unit, so I added && statement to validate the slotElementId.

  // Execute callback when the slot is visible in DOM (thrown before 'impressionViewable' )
  if (onSlotRenderEnded) {
    googletag.cmd.push(() => {
      googletag.pubads().addEventListener('slotRenderEnded', (event) => {
        // check if the current slot is the one the callback was added to
        // (as addEventListener is global)

        if (event.slot.getAdUnitPath() === path && event.slot.getSlotElementId() === id) {
          onSlotRenderEnded(event);
        }
      });
    });
  }

Also, when the Ad component unmounts, the event handler do not get removed. So it would be a good idea to remove the event handler in componentWillUnmount.