This example seems to have been broken by the switch to Typescript. We can't
just symlink in `../..` because that gives us the typescript version of the
source, which, obviously, doesn't work in node.
Instead, make sure we use a prebuilt version of the js-sdk.
It's actually even more broken as of js-sdk 33.0.0, thanks to the switch to ES
modules (#4187), but we'll get to that later.
We now rely on browserify for building browser-specific versions of the JS
SDK. This can be initiated by running 'npm run build-js'. Node versions are
unaffected.