Docs: SSR-ed page has missing assets

I’m seeing missing assets in the dev console but not visually on the page once it's up and running. I’ve checked and I get this:

1. in production currently
2. locally on master and
3. previous master before I merged the long running branch.

## Reproduction

```sh
$ cd docs
$ yarn && yarn clean && yarn build
$ yarn serve
```

Navigate to `http://localhost:4000/open-source/spectacle/` and then look at dev console for lots of 404 assets like our `.webm` preview.

## Notes

There are no visual effects, so what my theory is is that our SSR page has broken assets that we don’t see because client-side takes over before it’s noticeable. For an example, we have this component:

```jsx

Code Preview







```

It uses this data:

```js
preview: {
bgMp4: require('../../assets/demo-presentation.mp4'),
bgStill: require('../../assets/demo-still.png'),
bgWebm: require('../../assets/demo-presentation.webm'),
demoUrl:
'https://raw.githack.com/FormidableLabs/spectacle/master/examples/one-page.html'
},
```

This translates to the following in SSR’ed HTML (when prettified)

```html

But if you look in the `dist/` directory there is no file whatsoever named `646e170b7206d8b395cde42f9072ac68.webm` using find.

Instead what we do have emitted is in relevant part this:

```
dist/
└── open-source
└── spectacle
├── static
│   ├── amazing.b764e718.svg
│   ├── bg_hero_feather.1b0b9393.jpg
│   ├── browserconfig.xml
│   ├── button.a7c17f7a.svg
│   ├── code-preview.6d24653a.svg
│   ├── demo-presentation.646e170b.webm
│   ├── demo-presentation.c8255381.mp4
│   ├── demo-still.5cffd269.png
│   ├── favicon-32.png
│   ├── logo_spectacle.7afbf241.png
│   └── site.webmanifest
```