:visible components throw error

[ThatJoeMoore]

Reproduction

Modify /examples/kitchen-sink/astro/pages/index.astro to add :visible to any component.

When the page loads, the following error will occur:

Uncaught TypeError: document.querySelector(...).item is not a function

Issue

Here's the generated JS that's breaking:

Array.from(document.querySelector('[data-astro-id="2245226923414180"]').item(0).children).forEach(child => o.observe(child))

It looks like #72 changed how the IntersectionObserver gets set up to support having multiple components:

https://github.com/snowpackjs/astro/blob/188541260acad5ccd6699f0a21d6da600860e74c/src/frontend/render/renderer.ts#L58

It's now expecting root to be a call to querySelectorAll instead of querySelector, but it's still querySelector:

https://github.com/snowpackjs/astro/blob/188541260acad5ccd6699f0a21d6da600860e74c/src/frontend/render/renderer.ts#L23

As far as I can tell, all of the renderers are expecting root to be a call to querySelector, and the IntersectionObserver bit is the only part of the generated code that expects querySelectorAll. It seems like reverting the change to this line would fix :visible, but as I don't really know the context of the previous change, I don't know what else that might break.