fix(website): Fix infinite loop in scenegraph example

[donmccurdy]

Currently the scenegraph example makes infinite continuous requests for all.json locally for me. On the production website I'm not seeing anything because the OpenSky API returns 429s, but it might be that my IP address has just been rate limited.

I think the current behavior leads to continuous requests, because data is assigned in the loop callback, but data is also a dependency of the effect so these changes trigger more requests. I've refactored a bit and this fixes the issue locally, but I'm still blocked by the OpenSky API and can't test with real data.

Aside - Given that it only updates every 60s, maybe it'd be simpler (for purposes of showing a scenegraph example) to make a single request and skip the refresh cycle?

[coveralls]

coverage: 91.626%. remained the same
when pulling e314d5a on donmccurdy/fix-scenegraph-example-infinite-loop
into 81371bf on master.

[felixpalmer]

Aside - Given that it only updates every 60s, maybe it'd be simpler (for purposes of showing a scenegraph example) to make a single request and skip the refresh cycle?

I think the focus of the examples should be to showcase cool functionality, even at the expense of more complex code. It's nice to have it to example of live data with transitions. The docs already have a minimal example