Fix JS not executing after injecting Facebook SDK

I ran into #75 and did a little investigation given what the thread was saying. It was definitely the Facebook SDK injection which was causing trouble. It turns out if I commented out the line adding the `fb-root` element, JS kept running.

So instead of adding the element with `+=` I did it nicely with appendChild and now it seems to work.

The contributing guide didn't say if I should include the `.js` files so I didn't but they will be on the master branch of my repo. I can push them on this branch if you like.