errorComponent and loadingComponent options don't allow functions

[olgertse]

This makes it impossible to use React functional components in errorComponent or loadingComponent options.

[theodorDiaconu]

@od1k good point.

[justbill2020]

👍 bumping this... Looks like this was broken when poll option was added...

https://github.com/cult-of-coders/grapher-react/blob/master/lib/checkOptions.js#L9-L10